
Runrafter |
2 people marked this as a favorite. |

Hi All
I want to give the players a taste of the above. The players will be defending, trying to repel an orc assault.
How will the rules work with regard to this? I can see a few things:
1. logically players may ready an action as they stand by at the top
as the ladders fall into place. How do we handle throwing down a ladder?
2. When the attacking orcs get to the top of the ladder -- things look a bit grim,. but then apparently there is never a shortage of orcs. I figure the best they can hope to do is bull rush to make a space and get off the ladder ASAP, and let some mates up.
3. As they attempt to bull rush, the defenders get an attack of opportunity.
4. If the orcs are injured in the round, this decreases their combat maneuver bonus by the amount of damage. if the defenders are injured in the round -- does this decrease their combat manuever defence? Why not?
5. If the orc does not succeed in the bull rush -- I guess it would be nice to be able to push him (or her, gender equality even in death) off the ladder. I was thinking of calling this a trip manuever. I figure if they have taken damage that round, it should mean a decrease to their combat maneuver defence.
Am I on the right track? Suggestions? Answers to my question about throwing down the ladder?
Thanks!!!!

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Some of the orcs should already be on the ladder as it being raised. Thus they've no need to climb up and can just jump off and start killing. I'd suggest watching the Battle of Helms Deep on the Two Towers for further ideas.
Mechanically I don't see a problem thus far. But where did you get that taking damage lowers your CMB or CMD? I'd leave that out entirely being as it appears no where in the rules.
As for the actually pushing the ladder I'd either make it a STR Check or a Combat Manuever.
Something to be ready for is players in the first few rounds are going to be readying actions to attack the orcs, if they don't have ranged weapons. Make sure your orcs have at least a few class levels so they can take a few hits so they don't die once they reach the top, otherwise this will be a lack luster fight.
Another suggestion is to make sure you have lots of ladders going up at once, in order to increase orcs getting to the top of the wall. You can also have them employ siege towers. This will negate the need for ladders and your orcs can just burst forth and start slaughtering the would-be defenders.

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1. Throwing down a ladder: No rules on this. STR check it.
2. Sounds legit. Try showering the wall with ranged attacks first to clear it a bit.
3. Defender. Not plural. Only the target gets AoO.
4. What? No. Why? The CMB takes a hit because the defender is trying to stop him from bull rushing (and hurt the orc). The defender taking a hit would be incidental, the same as the attacker taking a hit from someone else who happens to hit when the orc tries to bull rush (most likely from readied action). That non-AoO incidental damage does not decrease the CMD or CMB.
5. Failing a bull rush does not result in further penalty. However, when climbing, taking damage forces an immediate climb check. Climbing a ladder should be a DC 0 though. Bull rush and trip will work well, and remember that while climbing, you can't use a shield and you loose DEX bonus.
You might try asking this in homebrew or advice. Sources...
"If you are hit by the target, you take the damage normally and apply that amount as a penalty to the attack roll to perform the maneuver." ... "Unless otherwise noted, performing a combat maneuver provokes an attack of opportunity from the target of the maneuver." ... "If you do not have the Improved Bull Rush feat, or a similar ability, initiating a bull rush provokes an attack of opportunity from the target of your maneuver."
"You need both hands free to climb, but you may cling to a wall with one hand while you cast a spell or take some other action that requires only one hand. While climbing, you can’t move to avoid a blow, so you lose your Dexterity bonus to AC (if any). You also can’t use a shield while climbing. Anytime you take damage while climbing, make a Climb check against the DC of the slope or wall. Failure means you fall from your current height and sustain the appropriate falling damage."

Eridan |

1) Make a strengh check. PCs on the wall against some orcs on the ground who are holding the ladder in place. Maybe the orcs have some grapple hooks etc. to get a bonus for this check. The PCs have to cut the ropes first ..
2) Bull rush, Reposition, Overrun or Arcobatics (Move through an enemy's space) to enter the wall are good ideas. Some "siege orcs" maybe are trained for this special purpose and have the related "Improved..." Feats. Additionally you can use this :
If your target is immobilized, unconscious, or otherwise incapacitated, your maneuver automatically succeeds (treat as if you rolled a natural 20 on the attack roll).
I think Tanglefoot Bags are a good way to immobilize some guys on the wall.
3) Yes but see 2)
4)
If you are hit by the target, you take the damage normally and apply that amount as a penalty to the attack roll to perform the maneuver.
You only get a penalty to your CMB if you are hit by the AoO. See 2) to avoid this.
5) By raw the orcs are climbing as long as they stay on the ladder.
Anytime you take damage while climbing, make a Climb check against the DC of the slope or wall. Failure means you fall from your current height and sustain the appropriate falling damage.
A trip attack is another good idea.Success = orc falls down but the orcs dont get a penalty due to damage (by RAW but you are the GM).
Use some orcs with climb speed via spells, potions of spider climb or special ability (some rogue can do that)

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put some hooks on the ladders so when they hit the wall, the defenders cannot just push them off. They must first disable the hooks (a good reason for Disable Device- the hooks snap into place, a locking pin holds it there, and cannot just be knocked loose).
As Madclaw said some orcs should already be on the ladders when being raised so they are ready to attack as soon as the ladder locks into place.
Good initial actions for the orcs will be Bull Rush and Overrun. The important thing is getting off the ladder and onto the wall.
A cruel thing would be modifying the Reposition maneuver. Simply remove the rule that you cannot reposition an opponent into an inherently dangerous space. This would allow your orcs to grab defenders and pull them off the walls, screaming as they fall to their deaths (or probably not since they will only take a few d6 damage- but maybe killed by the horde on the ground). Under this situation it seems perfectly fair to me.
I would definitely not use anything with damage lowering CMB and CMDs.
To knock an orc off the ladder, you could use Trip, the modified Reposition, or just make a generic Combat Maneuver to push them off.
Oddly I just had this weird vision in my head of the battle scene and in this scene there were balloons floating over the castle with goblins dropping burning oil on the castle defenders, and some of the floating goblins would cut the ropes to the balloons and they would fall into the ranks of the defenders. Half of them that fall just die on impact, but do some damage to the defenders. The defenders are then split between shooting at orcs and goblins.
Oh oh oh and the orcs put trolls in catapults and shoot them over the walls! The trolls splatter on the other side, then regenerate and begin attacking from inside. Oh man I wanna run this so bad!

Runrafter |

Now we are cooking wih gas!! Or, rather, frying orcs with oil.
better and better, the deeper we delve.
I've also been considering this battle and how the characters fit into it. I'm just not intersted in turning this into a mass combat for the characters. I think they will enjoy it more if they are not comanding something large, but are small players in a massive struggle -- maybe doing their job but also trying to survive.
So I was intending to lay out the general flow of what they see of the battle (a battle actually very like helm's deep), with crises that they need to respond to that may (or may not) be pivotal to the whole
battle. An intersting mix -- I want them to feel powerless one minute and like they can do something the next. No intention of crushing them
just want them to think they are about to be swatted like flies.
Say, they get things under control just where they are - but an adjacent wall is about to be overrun. Or a gallery ram is about to be brought up against a weekened partof the wall. Volunteers could be called to sortie from the sallie gate.
So I play out what they deal with, and what they do has a real effect on the outcome of the battle.
Any suggestions in regard to this big picture stuff?
Fantastic suggestions, thanks.

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3 people marked this as a favorite. |

I would like to contribute custom Mob rules, designed by a internet figure named Oslecamo. I've tested this template, it works. Mages beware. It won't work with the trickling in orcs, but it'll do great for 20+ 'mobs' of orcs. One good sized mob will make them battered, bloody and calling for the healer. I change the DR from armor to include Dex.
Well, as any D&D player may have noticed, it's really hard to make large number of small enemies threaten players once they start reaching higher levels.
It would be really cool if you could put your 10th level party against a hundred level 1 orc warriors, but the batle would be really one sided as the casters fly and drop nukes and the orcs can, at best, hit the party members on nat 20s, plus no sane DM wants to roll attacks, saves and iniatives for one hundred orcs, not to mention the models.
And the players wouldn't even get experience.
The good news is that DMG 2 gave us the mob template, wich turns that group of commoners into actualy something dangerous.
The bad news is that, like everything else in DMG2, it kinda sucks. Ok, it's probably the best thing in the book, and the only reason any D&D player should bother reading it, but the template itself really could use some work. It's a great idea and so I decided to properly polish it.
So I present you:
Mobs(template)
An angry mob represents a group of creatures that band togheter with a single destructive mentality. Like killing someone or taking down a city.
A mob is treated as a single entity similar to a swarm,
except that it is made of larger creatures. A mob can be
composed of Small, Medium, or Large creatures, but all
the individual creatures must be of the same type. A mob
that incorporates a crowd of goblins and a crowd of chokers
is best modeled by two separate mobs.
“Mob” is an acquired template that can be added to any
group of Small, Medium, or Large creatures who choose to form a mob. A mob uses all the base creature’s statistics and special abilities except as noted here.
Unless noted otherwise, all of the mob abilities are ex abilities.
Resumed version:
Size: dependant on the number of members. Large ones count as four and small ones count as half. Mobs have reach as the base creature.
8-20: large
21-37: huge
38-68: gargantuan
69-128: colossal
Other creatures can move across a mob whitout troubles, and the mob can move over creatures, causing attacks of oportuny for movement. Mobs do attacks of oportunity as their base creature does, except that they have no limit to the number of aoos they may perform per turn. Mobs can change their shape at will as long as their area remains the same and pass trough any passage large enough to allow passage of their composing inidividuals.
HD:Equal to the number of members. Mobs breack up at 0 hp.
Speed:reduce by 10
The following remain unchanged from the base creature, but apply the mob's size modifier: AC, grapple
The following remain unchanged from the base creature:
Iniative, BAB, saves, physical stats, skills, attack options that don't demand an activation like poison, and any ability that's based on the total number of HD of the creature
Charisma, intelegence and wisdom change to 10.
Mob damage: die damage of the weapon most common on the mob, increased to the new size, and multiplied by the following factor based on the mob's size. Apply strenght modifier before multiplier.
1/2 BAB:Don't multiply
3/4 BAB: multiply by 2
Full BAB:multiply by 3
Armor and shield bonuses count as DR against all mob attacks.
Mob attack options:
Mob up: mobs automaticaly deal mob damage to all creatures in the same area of the mob at the end of the mob's turn, whitout need of any action. It may also choose to attack objects whitin it's reach as a free action at the end of their turn.
Voley:Standard action, single target or area based on mob size. Uses mob's ranged weapons range. Ref save for half damage of 10+mob's dex+mob's BAB.
If the mob has enough BAB it can do iterative attacks as a fullround action, but only against a single target. Range increment penalties apply to the save DC.
Large:Can't use area attack.
Huge-5 radius circle.
Gargantuan-10 radius circle.
Colossal-20 radius circle.
Creatures hit by a volley get can't move next turn and drop twice the damage they've taken in feets if they're flying. A sucessfull save means hit creatures move at half speed next turn and drop the damage taken in feets if flying.
Volleys cannot be used if the mob has ungrappled enemies inside of it.
Mob grapple: as normal grapple, but creatures who are caught by the mob take mob damage instead of unarmed damage, and the mob can never be grappled itself. It can also carry grappled creatures at it's full speed. A mob who's grappling a target never takes any penalty for grappling.
Trample:The mob must start and end it's turn away from the creature, passing over it somewhere in between. Damage 2d6+1,5 str modifier of the mob, reflex DC 13+mob's size bonus+mob's strenght modifier for half damage. Enemies can choose to make an aoo instead of the save. Only smaller creatures than the mob are affected.
Mob mind:A mob cannot use any special ability that demands an activation like spells and breath attacks. It can still use abilities that work automaticaly such as poison, improved grappled, swallow whole, gaze attacks ect. Use the base creature HD for DCs
Mobs can still use skills as normal.
Mob Anatomy:Immune to criticals, precision damage and spells/effects that don't deal damage and/or don't outright kill a creature.
Don't affected by flanking, bullrush, overrun, trip or grapple
If a mob fails a save against a spell/effect that would normally kill/incapapacitate a creature, such as disintrigate, slay living or wail of the bashee, it instead gains one negative level for each creature that would be killed by that spell/effect. Large creatures count as 4 and small creatures count as half.
Mobs take +50% damage from area damage spells.
Mobs take double damage from melee attacks from creatures with cleave.
Mobs take quadruple damage from melee attacks from creatures with greater cleave.
Feats: Same as the base creature; all mobs gain Improved
Bull Rush and Improved Overrun as bonus feats.
Challenge Rating:
Large:3, or +2 if the base creature’s CR is 2 or higher.
Huge:5, or +2 if the base creature’s CR is 4 or higher.
Gargantuan:8, or +2 if the base creature’s CR is 7 or higher.
Colossal:12, or +2 if the base creature’s CR is 11 or higher.
New:
Unit (http://www.giantitp.com/forums/showpost.php?p=7325672&postcount=27), a more organized form of the mob.
Leaded Mob (http://www.giantitp.com/forums/showpost.php?p=7195979&postcount=17)
Detailed version
Size and Type:
Size is based on the number of creatures forming the mob. Large creatures count as four, and small creatures count as half. It is assumed that the creatures press against each other, and thus they fill less space than they would fill as individuals. There must be at least 8 members to form a mob. Mobs with more members than the maximum size should be represented as multiple mobs. The mob’s type remains unchanged from the base creature.
8-20: large
21-37: huge
38-68: gargantuan
69-128: colossal
Hit Dice:
A mob has a single pool of Hit Dice and hit
points. Like regular HP, it's an abstraction of both the endurance of the members of the mob and their will to destroy whatever it's on their path.
The mob has HD equal to the number of composing members (with large creatures counting as 4 and small creatures counting as half).
Reducing a mob to 0 hit points or lower causes it to
breack up (with two thirds of it's members killed or disabled, the remaining undamaged, but now counting as simple individuals, and probably wanting to run away for their lifes), though damage taken until that point does not degrade its ability to attack or resist attack. Mobs are never staggered or reduced to a dying state by damage.
However, for abilities based on the number of HD, like SR, the mob uses the number of HD of the base creature.
Initiative: As the most common among the creatures composing the mob.
Speed: A mob’s speed is 10 feet slower than that of the
base creature.
Armor Class: As the base creatures, with the respective penalty for the new size(-1 for large, -2 for huge, -4 for gargantuan, -8 for colossal)
If the creatures have diferent kinds of AC, use the most common.
Base Attack:Use the most common BAB of the members of the mob. Don't recalculate based on the new HD.
Grapple: Use the base creature attack bonus, modified for the mob's size, and as appropriate for its Strength modifier.
Attack/Full Attack: Mobs can’t make standard attacks. In return, they receive three special attack options:
Mob up
A mob automaticaly deals damage to any creature whose space it occupies at the end of its move, with no attack roll needed. Mob attacks ignore concealmentand cover. A mob’s attacks are nonmagical, unless the
base creature’s attacks are considered magical. Damage reduction applies to mob up attacks.
The damage amount and type is based on the damage the most common kind of individual of the mob would normaly deal, but multiplied by a factor based on it's BAB and increase the damage HD acording to the new size.
1/2 BAB:Don't multiply
3/4 BAB: multiply by 2
Full BAB:multiply by 3
For example, a mob of 50 orc warriors with longswords would deal 12d6+6 damage to any creature inside it every turn.
The mob can also choose to deal that damage to any unatended object it is touching. So a mob could eventualy bring down walls and houses.
Volley
If at least half of the members of the mob have similar ranged weapons, they can fire at the same time at an area or target as a standard action. The mob cannot fire if it has nongrappled enemies on it's midst.
Range is the same as the ranged weapon more common in the mob. Damage is as the mob up attack, but based on the ranged weapon the mob is using. Range increments give a bonus on the defender's save of +2 for each range increment.
Single target: as mob up attack damage, enemy can make a reflex save equal to the mob's BAB+ 10+mob's dex modifier for half damage. If using a fullround action the mob can do iterative attacks, but whitout the -5 penalty.
Area attack: A mob of huge size or larger, as a fullround action, can deal mob up damage in an area based on their own size. Reflex of 10+BAB+mob's dex modifier for half.
Huge-5 radius circle.
Gargantuan-10 radius circle.
Colossal-20 radius circle.
Creatures who fail their saves against a volley of either kind are pinned down by the projectiles, and cannot move next turn. If flying, they drop down twice as much feets as they took damage.
Even if they make their saves, their speed is reduced to half in the next turn, and if flying they drop a number of feets equal to the damage taken.
Mob grapple: a mob can grapple as a standard action, altough it cannot be grappled back. Sucessfull rolls from the oponent just mean it managed to don't be brought down by the mob. Instead of unarmed damage, the mob deals the mob up attack damage to grappled oponents as they are mercyless steped over by the angry individuals. The mob can carry grappled oponents at it's full speed.
Armor and shield bonus work as DR against all mob damage.
Space/Reach:
Large-10 by 10 feets square
Huge-15 by 15 feets square.
Gargantuan-20 by 20 feets square.
Colossal-30 by 30 feets square.
A mob's reach is the same of the base creature, and it's aoos work exactly as aoos from that creature, except the mob can make as much aoos per turn as it wants. It's height is the average of the composing individuals.
In order to attack, it moves into an opponent’s space, which provokes an attack of opportunity. It can occupy the same space as a creature,
since it tramples over and moves around its victim. A mob
can move through squares occupied by enemies, and vice
versa, without impediment, although a mob provokes an
attack of opportunity if it does so. A mob can move through
openings large enough for its component creatures.
The area occupied by mobs is completely shapeable,
though the mob usually remains in contiguous squares.
Mob mind:
A mob’s mentality is fueled by emotion;
as a result, the individual creatures that make up
the mob are unable to use any attack options that require
actions, such as breath weapons, spell-like abilities, and
the like. If the base creature has attack options that affect
the damage it deals (such as poison, energy drain, abilitydamage, improved grab, constrict, rend, or swallow whole),
those special attacks function normally on any creature
damaged by the mob. Attack options such as gaze weapons
that function constantly continue to function normally.
The save DCs for any of these attacks should be recalculated
based on the mob’s Hit Dice.
Mobs can still use skills as normal.
In addition, mobs gain both of the following:
Expert Grappler (Ex): A mob can maintain a grapple without
penalty and still make attacks against other targets
(normally, attacking other targets while grappling imposes
a –20 penalty on grapple checks). A mob is never considered
flat-footed while grappling.
Trample (Ex): A mob that simply moves over a creature
and doesn’t end its movement with that creature in one of
its occupied squares can trample the creature. The creature must be at least one size smaller than the mob. A trampled creature takes damage equal to 2d6 points + 1,5 times the mob’s Strength modifi er. The victim can either make an attack of opportunity against the mob or make a Refl ex save (DC 13+mob's size bonus+the mob’s Str modifi er)to take half damage.
Special Qualities: A mob retains all the special qualities
of the base creature. In addition, it gains the following
special quality.
Mob Anatomy (Ex): A mob has no clear front or back
and no discernible anatomy, so it is not subject to critical
hits or sneak attacks. A mob cannot be flanked, tripped,
grappled, or bull rushed.
However, unlike standard swarms, mobs are made up of relatively
small numbers of individual creatures, so spells or
effects that target specific numbers of creatures can have
an effect on a mob. Each specific creature that is slain,
disabled, or otherwise incapacitated by spells or effects
that target specific creatures bestows one negative level
on the mob.
A mob that gains negative levels equal to its
Hit Dice breaks up as if reduced to 0 hit points. Negative
levels gained in this manner are not the result of negative
energy (and thus cannot be blocked by death ward or
removed by restoration), but never result in permanent
level loss. A mob takes half again as much damage (+50%)
from spells or effects that affect an area, such as splash
weapons and evocation spells.
Characters with cleave deal double damage to a mob in melee. Characters with greater cleave deal quadruple damage to a mob in melee.
Saves: A mob uses the same saving throws as the base creature, but failed saves never result in anything worst than negative levels as it loses members. Effects that don't instantly disable a creature (like blindness or curse) have no effect whatsoever on the mob.
Abilities: A mob’s abilities are the same as the base
creature, except that its Intelligence, Wisdom, and Charisma
scores drop to 10. If the base creature’s Intelligence,
Wisdom, or Charisma scores are already lower than 10,
they do not change.
Skills: Same as the base creature; do not recalculate
based on the mob’s new Hit Dice. The mob’s new Intelligence,
Wisdom, or Charisma scores might grant some
skills different modifiers.
Feats: Same as the base creature; all mobs gain Improved
Bull Rush and Improved Overrun as bonus feats.
Challenge Rating: Based on size:
Large:3, or +2 if the base creature’s CR
is 2 or higher.
Huge:5, or +2 if the base creature’s CR
is 4 or higher.
Gargantuan:8, or +2 if the base creature’s CR
is 7 or higher.
Colossal:12, or +2 if the base creature’s CR
is 11 or higher.

Kimera757 |
Hi All
I want to give the players a taste of the above. The players will be defending, trying to repel an orc assault.
How will the rules work with regard to this? I can see a few things:
For starters, whoever is defending the castle has huge advantages. Really, they only need to worry about running out of food, and disease. They can throw rocks and fire at the orcs all day. The orcs should only try storming the walls as a distraction for their real plan.
Of course, the PCs cannot possibly defend the entire walls, and the orcs might even sneak a ladder (concealed with magic?) somewhere against the castle. Or maybe a spellcaster can turn invisible and simply climb the wall with Spider Climb. (During the battle, the gates might come unlocked, and the PCs might have to rush to keep the orcs out... leaving the walls relatively unguarded.)
1. logically players may ready an action as they stand by at the top as the ladders fall into place. How do we handle throwing down a ladder?
I figure shoving an orc off the ladder isn't too hard (readied bull rush), but the DC for shoving the ladder should be determined by you. It should be hard. It'd take several characters to do, usually.
2. When the attacking orcs get to the top of the ladder -- things look a bit grim,. but then apparently there is never a shortage of orcs. I figure the best they can hope to do is bull rush to make a space and get off the ladder ASAP, and let some mates up.
Orcs need help here. I figure a good dose of intimidation, or maybe fire, will help. Or better yet, Improved Overrun! (Knock over a bunch of guys, and now you're inside.) Once a few orcs have gotten on top, it's time for them to start bull rushing humans off the walls. Or just hacking, whatever works. Against the generic warriors who are likely trying to protect the castle, the orcs should be cutting through them and quickly too.
3. As they attempt to bull rush, the defenders get an attack of opportunity.
Specially trained orcs with Improved Bull Rush would help here, as they don't provoke an opportunity attack. Maybe only one per ladder. Make them barbarians. That'll really crank their Strength bonuses (and I think they get a bonus to CMB from Improved Bull Rush too).
Also, Improved Overrun is handy here. Probably even better than Improved Bull Rush, because you can't bull rush someone through their friends, but you can just stomp on some humans.
4. If the orcs are injured in the round, this decreases their combat maneuver bonus by the amount of damage. if the defenders are injured in the round -- does this decrease their combat maneuver defence? Why not?
This has no effect. An orc who keeps failing to bull rush (or overrun) without the appropriate feat will run out of hit points. Eventually.
5. If the orc does not succeed in the bull rush -- I guess it would be nice to be able to push him (or her, gender equality even in death) off the ladder. I was thinking of calling this a trip manuever. I figure if they have taken damage that round, it should mean a decrease to their combat maneuver defence.

Runrafter |

Thanks for those very interesting mob rules.
I'm going to be running this game on Friday -- and would like to implement the mob rules.
I've run aground, however, in that I cannot under stand the damage component:
The damage amount and type is based on the damage the most common kind of individual of the mob would normaly deal, but multiplied by a factor based on it's BAB and increase the damage HD acording to the new size.
1/2 BAB:Don't multiply
3/4 BAB: multiply by 2
Full BAB:multiply by 3.
Could you help me understand this? It looks like something is missing.
What is the significance of 1/2 BAB -- and when? Same for the other levels in this list.Your help is much appreciated.
Kind regards
Nimrodx

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A mage has 1/2 BAB. A rogue has 3/4 BAB. A fighter has full BAB. This is relevant to reflect the martial prowess of the mob- a group of paladins will hit harder with their swords than a group of commoners with similar swords.
Orc warriors use full BAB, so multiply by 3.
Note: Tell your players that while they're facing low-level orcs, they are a threat and are using mechanics they are unfamiliar with, and will get appropriate XP/rewards.

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This is a homebrew mechanic I have used once before for a large battle. Set an arbitrary number of rounds based on cr of enemies in the PC's immediate vicinity. (cr - apl + 3 is what I used) Do not tell the PC's this number. If the pc's defeat the group in less time, they are starting to turn the tide in their favor and can take a moment to direct NPC's nearby where they are needed most (We need more archers on the southern walls!) If they tie, they are merely holding ground. If they take more time than allotted, NPC's arrive to help, but then a leak in the defense opens somewhere down the line. Now the party has to deal with the leak, and give them another number of rounds to accomplish it. After enough losses, things can get really bad, and the reserves get called in to fight the big bad evil thingy that made its way into the castle/onto the walls. Oh, and when the PC's continue winning a lot? Orcs ain't stupid when it comes to warfare. They can do the same. Give the PC's more enemies to fight as they continue doing well. Also, award ingenuity with more rounds. "All we have is this wand of invisibility? Fine, use it on the catapult ammunition before we fire!" Maybe not RAW, but I'd allow it just to see a bunch of orcs go splat from an invisible boulder.
If you want to REALLY give the players something different, let them go on the offensive. A handy teleport behind enemy lines, followed by some chaos, running away, and teleporting back/somewhere else would make for some very interesting battlefield confusion.
As would a nicely charmed goblin balloon.
Or a goblin balloon on fire, going the wrong way.
Or a goblin on fire, going the wrong way.