I believe I understand the basics of creating a monster from scratch, and I know of the chart that lists suggested baseline capabilities for a monster at a given CR. But what about when exotic special abilities come into play?
I'm sure most monsters are expected to have their share of special abilities. Some abilities will be game-changers, and others are far less emphatic. I'd imagine having a lot of different abilities that can only be used one at a time would eventually amount to clutter. How can I know, though, if a special ability warrants an adjustment to a monster's CR, and how great of a change it would be?
Consider the following homebrew monster as an example. His CR (and XP) is left blank for now. (Also let me know if you spot any math errors.)
This hovering orb of metallic debris churns and whirls as it floats through the air.
SPECIAL ABILITIES
Magnetic Aura (ex)
A small Magnetic Elemental radiates a magnetic aura. All metal creatures and creatures wearing metal armor within 10 feet of the elemental are slowed (as the slow spell.) See the table below for the area each elemental affects.
Magnetic Surge (ex)
As a standard action once every 1d4+1 rounds, a Magnetic Elemental can make a disarm attempt against all creatures within its magnetic aura. This ability only affects metal weapons and does not provoke attacks of opportunity. Successfully disarmed weapons are drawn to the elemental and cling to it without dealing damage to it. Creatures can attempt to remove such weapons with an opposed strength check as a standard action that provokes an attack of opportunity (the elemental can choose to take 10 on this check.)
Electromagnetic Surge (ex)
Whenever a Magnetic Elemental is targeted by an effect that deals electricity damage, it can use its Magnetic Surge ability as an immediate action. This does not effect the delay between normal uses of Magnetic Surge.
Seize Weapon (ex)
Whenever a Magnetic Elemental is damaged by a metal weapon, it can immediately make a disarm attempt against that weapon as a free action. Successfully disarmed weapons cling to the elemental. Creatures can attempt to remove such weapons with an opposed strength check as a standard action that provokes an attack of opportunity (the elemental can choose to take 10 on this check.)
Elemental Size Height Weight Aura Disarm
Small Small 4 ft 30 lb 10 ft +5
Medium Medium 8 ft 90 lb 20 ft +10
Large Large 16 ft 810 lb 30 ft +17
Huge Huge 32 ft 6000 lb 30 ft +22
Greater Huge 36 ft 6000 lb 40 ft +26
Elder Huge 40 ft 6000 lb 50 ft +30
ECOLOGY
Environment: any (Plane of Air)
Organization: solitary, pair, or gang (3-8)
Treasure: Double (metal items only)
Magnetic elementals are unsophisticated, stubborn creatures made of magnetic fields. They are concerned with little more than collecting metals, and favor opponents who wear armor or wield weapons made of metal.
The true body of a magnetic elemental appears as a transparent distortion in the air; the metal composing its form is merely debris that it has collected over its life. They can take a variety of different shapes, though they always maintain the same statistics. Unsuspecting adventurers often mistake them for a kind of earth elemental.
SMALL MAGNETIC ELEMENTAL
XP
N Small outsider (air, elemental, extraplanar)
Init +2; Senses: darkvision 60 ft; Perception +5
Aura: Magnetic aura (10 ft. radius)
DEFENSE
AC 17, touch 13, flat-footed 15 (+2 Dex, +4 natural, +1 size)
hp 13 (2d10+2)
Fort +4, Ref +5, Will +0
Defensive Abilities: Electromagnetic Surge, Seize Weapon; Immune: Electricity, elemental traits
OFFENSE
Speed: Fly 50 ft. (average)
Melee: Slam +5 (1d6+2)
Special Attacks: Magnetic surge (Disarm +5)
STATISTICS
Str 15, Dex 14, Con 13, Int 4, Wis 11, Cha 11
Base Atk +2; CMB +3; CMD 15
Feats: Improved Disarm (B), Power Attack
Skills: Acrobatics +6, Escape Artist +6, Fly +8, Knowledge (planes) +1, Perception +5
Languages: Auran
MEDIUM MAGNETIC ELEMENTAL
XP
N Medium outsider (air, elemental, extraplanar)
Init +3; Senses: darkvision 60 ft; Perception +7
Aura: Magnetic aura (20 ft. radius)
DEFENSE
AC 18, touch 13, flat-footed 15 (+3 Dex, +5 natural)
hp 34 (4d10+12)
Fort +7, Ref +7, Will +1
Defensive Abilities: Electromagnetic Surge, Seize Weapon; Immune: Electricity, elemental traits
OFFENSE
Speed: Fly 50 ft. (average)
Melee: Slam +8 (1d8+4)
Special Attacks: Magnetic surge (Disarm +10)
STATISTICS
Str 19, Dex 16, Con 17, Int 4, Wis 11, Cha 11
Base Atk +4; CMB +8; CMD 21
Feats: Cleave, Improved Disarm (B), Power Attack
Skills: Acrobatics +8, Escape Artist +8, Fly +8, Knowledge (planes) +2, Perception +7
Languages: Auran
LARGE MAGNETIC ELEMENTAL
XP
N Large Outsider (air, elemental, extraplanar)
Init +9; Senses: darkvision 60 ft; Perception +11
Aura: Magnetic aura (30 ft. radius)
DEFENSE
AC 20, touch 13, flat-footed 16 (+4 Dex, +7 Natural, -1 Size)
hp 76 (8d10+32)
Fort +10, Ref +10, Will +2
Defensive Abilities: Electromagnetic Surge, Seize Weapon; DR 5/-; Immune: Electricity, elemental traits
OFFENSE
Speed: Fly 50 ft. (average)
Melee: 2 slams +13 (2d6+6)
Space: 10 ft; Reach: 10 ft
Special Attacks: Magnetic surge (Disarm +17)
STATISTICS
Str 23, Dex 18, Con 19, Int 6, Wis 11, Cha 11
Base Atk +8; CMB +15; CMD 29
Feats: Cleave, Great Cleave, Improved Disarm (B), Improved Initiative, Power Attack
Skills: Acrobatics +13, Escape Artist +13, Fly +13, Knowledge (planes) +5, Perception +11
Languages: Auran
HUGE MAGNETIC ELEMENTAL
XP
N Huge Outsider (air, elemental, extraplanar)
Init +10; Senses: darkvision 60 ft; Perception +13
Aura: Magnetic aura (30 ft. radius)
DEFENSE
AC 21, touch 14, flat-footed 15 (+6 Dex, +7 Natural, -2 Size)
hp 105 (10d10+50)
Fort +12, Ref +13, Will +5
Defensive Abilities: Electromagnetic Surge, Seize Weapon; DR 5/-; Immune: Electricity, elemental traits
OFFENSE
Speed: Fly 50 ft. (average)
Melee: 2 slams +16 (2d8+8)
Space: 15 ft; Reach 15 ft
Special Attacks: Magnetic surge (Disarm +22)
STATISTICS
Str 27, Dex 22, Con 21, Int 6, Wis 11, Cha 11
Base Atk +10; CMB +20; CMD 36
Feats: Cleave, Great Cleave, Improved Disarm (B), Improved Initiative, Iron Will, Power Attack
Skills: Acrobatics +17, Escape Artist +16, Fly +15, Knowledge (planes) +6, Perception +13
Languages: Auran
GREATER MAGNETIC ELEMENTAL
XP
N Huge Outsider (air, elemental, extraplanar)
Init +10; Senses: darkvision 60 ft; Perception +16
Aura: Magnetic aura (40 ft. radius)
DEFENSE
AC 22, touch 14, flat-footed 16 (+6 Dex, +8 Natural, -2 Size)
hp 149 (13d10+78)
Fort +14, Ref +14, Will +6
Defensive Abilities: Electromagnetic Surge, Seize Weapon; DR 10/-; Immune: Electricity, elemental traits
OFFENSE
Speed: Fly 50 ft. (average)
Melee: 2 slams +20 (2d10+9)
Space: 15 ft; Reach 15 ft
Special Attacks: Magnetic surge (Disarm +26)
STATISTICS
Str 29, Dex 22, Con 23, Int 8, Wis 11, Cha 11
Base Atk +13; CMB +24; CMD 39
Feats: Awesome Blow, Blind-Fight, Cleave, Great Cleave, Improved Disarm (B), Improved Initiative, Iron Will, Power Attack
Skills: Acrobatics +22, Escape Artist +22, Fly +18, Knowledge (planes) +15, Perception +16
Languages: Auran
ELDER MAGNETIC ELEMENTAL
XP
N Huge Outsider (air, elemental, extraplanar)
Init +10; Senses: darkvision 60 ft; Perception +19
Aura: Magnetic aura (50 ft. radius)
DEFENSE
AC 24, touch 16, flat-footed 18 (+6 Dex, +10 Natural, -2 Size)
hp 200 (16d10+112)
Fort +17, Ref +16, Will +7
Defensive Abilities: Electromagnetic Surge, Seize Weapon; DR 10/-; Immune: Electricity, elemental traits
OFFENSE
Speed: Fly 50 ft. (average)
Melee: 2 slams +24 (2d10+10/19-20)
Space: 15 ft; Reach 15 ft
Special Attacks: Magnetic surge (Disarm +30)
STATISTICS
Str 31, Dex 22, Con 25, Int 10, Wis 11, Cha 11
Base Atk +16; CMB +28; CMD 44
Feats: Awesome Blow, Blind-Fight, Cleave, Great Cleave, Improved Critical (slam), Improved Disarm (B), Improved Initiative, Iron Will, Power Attack
Skills: Acrobatics +25, Escape Artist +25, Fly +21, Intimidate +19, Knowledge (planes) +19, Perception +19
Languages: Auran
This is the first homebrew monster I've made for Pathfinder. It's been years since I made one for 3.5, and I've only made four or five total, so I don't have a lot of experience with it.
Magnetic Elementals statistics run fairly close to other elementals, perhaps slightly higher in some cases. However, its special abilities can be a bit more emphatic than other similar elementals. Some PCs, such as a Fighter, will be hit hard, but Wizards and Druids probably wouldn't even notice. (I'm also considering the possibility of adding a racial bonus to Disarm.)
If you want to drag real-world physics into your game, its abilities would only affect metals qualified as ferrous. This means no coins, and it also means running through all of the fantasy metals and deciding which ones qualify and which ones don't. The Rusting Grasp spell has this qualifier, but the Rust Monster does not.
As I understand it, CR is a little all over the place to begin with. I was never entirely satisfied with that, as it directly determines XP yield. But still, CR is an important tool, even if it's only a ballpark figure, and I'd like to know more about how to handle it. Thanks in advance.
The best way to determine if an ability is appropriate for CR is compare the monster with other monsters or find monsters with similar abilities and see what their CR is. If not, then find a spell to compare the ability to.
Elementals do have set Crs, if you look in the bestiaries 1+2
The best way to determine if an ability is appropriate for CR is compare the monster with other monsters or find monsters with similar abilities and see what their CR is. If not, then find a spell to compare the ability to.
If you know of any monsters with comparable abilities, let me know. I did take a look at the Rust Monster, which can similarly screw over metal-bearing heroes, albeit on a more permanent basis. Rust Monster's capabilities are in line with a monster of its own CR, all except for its pitifully low damage output. Maybe I should reduce one of my monster's own stats to bring its CR in line with other elementals? Its AC perhaps?
Approaching the ability as a comparable spell, though, it does have the effect of a third level spell (slow), except that it offers no saving throw and it also can't be nullified with antimagic. But what do I do with that knowledge? Is a monster expected to have access to special abilities at the same HD that players gain roughly equivalent magic?Elementals do have set Crs, if you look in the bestiaries 1+2
Does that mean that any homebrew basic elemental should stay at the same CR as other elementals of the same magnitude?