Context: I am building a boss monster to put up against a group of four or five 11th level PCs with 1 mythic tier. Yes, I know that's not the advised mythic progression, story reasons. The campaign will have no full casters (ban hammer; it's a long story, but also story reasons). What I want to know is: fully healed and rested, do they have any chance of beating this thing? Specifically, what tactics would work against it? I am concerned it might be a bit too much to handle knowing nothing about it going in, and I'm open to advice on how I could balance it/subtly warn the PCs about the looming figure in their future.
Mythic Rune-Carved Lifespark Tiberolith (Bestiary 4 259, Ultimate Magic 115, Advanced Bestiary 191, Mythic Adventures 225)
CR 12/MR 5; XP 19,200
N Huge Construct (mythic)
Init +1/-19; Senses Darkvision 60ft., low-light vision; Perception +0
DEFENSE
AC 30, touch 9, flat-footed 29 (+1 Dex, +21 natural, -2 size)
hp 161 (13d10 + 90); fast healing 10
Fort +6, Ref +5, Will +4; -2 vs. mind-affecting effects; Second Save
DR 10/adamantine, bludgeoning, and epic; Defensive Abilities Block Attacks, Rune-Carved, Spell Trap; Immune acid, construct traits; Resist cold 15 fire 15, electricity 30, sonic 15; SR 29
Weaknesses Healing Immunity
OFFENSE
Speed 30ft.
Melee 2 Slams +21 (3d8 + 20/19-20)
Space 15ft; Reach 15ft.
Special Attacks Corrosive Strikes, Mythic Power (5/day, Surge +1d8), Rune of Agony, Rune of Terror, Shockwave
STATISTICS
Str 28, Dex 13, Con -, Int 7, Wis 11, Cha 1
Base Atk +13; CMB +24 (+28 Bull Rush); CMD 35 (39 vs. Bull Rush)
Feats Ability Focus (Shockwave), Awesome Blow, Great Fortitude, Improved Bull Rush (M), Improved Critical (Slam), Power Attack (M), Weapon Focus (M, Slam)
Skills Craft (stonemasonry) +14
Languages Common
SQ Accelerated Repair, Keyed Domains (Artifice and Rune), Open Mind, Spirit Within
SPECIAL ABILITIES
Accelerated Repair (Ex) As a full-round action, a lifespark construct can heal damage by jerry-rigging itself. The construct attempts an appropriate Craft skill check (DC 10). With a successful roll, the construct heals itself of 1d4 hit points of damage per number rolled above the DC. Accelerated repair provokes attacks of opportunity. If it wishes, the construct may make a standard effort to repair itself, but without the standard repair cost. This repair takes 1 day of constant work.
Corrosive Strikes (Ex) A tiberolith reduced to 30 or fewer hit points leaks acid, and deals an additional 1d6 points of acid damage with its slam attacks.
Healing Immunity (Ex) A lifespark construct cannot be affected by spells with the healing descriptor unless the spell specifically states it can affect constructs.
Keyed Domains (Ex and Su) The creature has fast healing 10 (from the Artifice domain) and is rune-carved (from the Rune domain). Whenever the creature takes energy damage or energy damage fails to overcome its SR, for the next round, its attacks deal 2d6 points of damage of that energy type. If more than one type of energy attack occurs in a round, roll randomly to determine what kind of extra energy damage it deals.
Open Mind (Ex) Lifespark constructs lack constructs’ usual immunity to mind-affecting effects, and in fact take a -2 penalty on saving throws against mind-affecting effects.
Rune-Carved The creature has been enhanced by the rune-carved construct modification. The Rune of Agony triggers the first time the creature takes damage. Creatures within a 20-foot-radius spread must succeed on a DC 17 Fortitude save or suffer from wracking pains that impose a -4 penalty on attack rolls, skill checks, and saving throws for 1 minute. On a successful saving throw, the creature takes the penalties imposed by the rune for 1 round. The Rune of Terror triggers the first time a creature moves adjacent to the creature, and creates a 20-foot-radius spread of necromantic energy that panics creatures within it for 1d4 rounds (Will DC 20 shortens to shaken for 1 round).
Shockwave (Su) Three times per day, a tiberolith can unleash a burst of electricity. This blast deals 12d6 points of electricity damage to all creatures within 30 feet (Reflex DC 18 half). A tiberolith is immune to its own shockwave and that of other tiberoliths. The save DC is Constitution-based.
Spell Trap (Su) When a tiberolith is targeted by a spell that allows spell resistance and its spell resistance fails to protect it against that spell, the spell instead becomes trapped in the tiberolith’s magical runes. The runes can only trap one spell at a time; if a second spell would become trapped, the first spell affects the tiberolith normally (including allowing a saving throw, if appropriate) and the second spell is trapped. A trapped spell dissipates harmlessly after 24 hours.
Spirit Within (Ex) Certain spells that rely on the existence of a creature’s soul- namely astral projection, clone, magic jar, and soul bind- can affect lifespark constructs. No other necromantic effects affect lifespark constructs, and they are still immune to death effects. Though they cannot be raised or resurrected, they can be reincarnated as described by the reincarnate spell.
Mythic Feats Mythic Improved Bull Rush grants a +2 bonus on checks to bull rush and to CMD against bull rush. Furthermore, the user can make an attack of opportunity against any creature that attempts to bull rush them, unless it also has this feat. Mythic Power Attack improves the bonuses by +1, and the bonus damage is doubled on a critical hit before being multiplied by the weapon’s critical modifier. The user can expend one use of mythic power when they activate Power Attack to ignore the penalties on melee attack rolls and combat maneuver checks for 1 minute. Mythic Weapon Focus doubles the bonus from Weapon Focus. As a swift action, they can expend one use of mythic power to gain a +2 bonus on attack rolls with the selected weapon until the end of their turn.
While this isn't precisely what you asked for, it's my best advice for building encounters;
Don't have single enemy encounters. It's very easy to slip off the edge onto 'destroys the party in one round' or 'the party destroys it in one round'. And even then, luck of the dice can force you to slip off anyway. The enemy rolled a 1 on a save-or-suck? Gone. The party wizard rolled a 1 on a save-or-suck? Gone.
I'd suggest that you make say three nerfed versions of this monster and send them against your party. Alternatively, have the monster split into smaller parts/versions of itself when it receives a certain amount of damage.
For some more specific advice...
Without knowing the party composition it's hard to tell if the DR is too much; if it's all archers could be an issue, if it's a bunch of greatsword-wielding barbarians, should be fine. But my gut feeling is that it is too tough, and its attacks are too dangerous for it to be taken down by this party.
I don't know how my party will build their characters because I don't have one, yet. This is as much theorycrafting as anything else. When I say "boss" monster, I'm more thinking "the huge thing in the innermost chamber of the dungeon" than "the thing in charge." Rune of Terror's in the Rune-Carved section after Rune of Agony.
Tactics that involve the PCs coming in with some kind of plan are...unlikely. I'm leaning away from informing them of anything about this creature ahead of time, so they're coming in cold. Perhaps that will prevent them from railgunning it to death in the first round. I keep forgetting that Clustered Shots is a thing. This is what I get for never having archer PCs.
I think offensively, it should be alright. The space I'm considering having this thing encountered (it's smart enough to know it can't kill birds it can't reach) has a thirty-foot ceiling and should be small enough for it to reach most corners in a move action or two.
As for it coming alone: I reached the same conclusion. Alone, they'd murder it in two rounds. I was thinking augmenting it by adding a handful of Arcane (the mythic simple template) Shadows or Wraiths to debuff and harass the party. Armed with, say...ray of enfeeblement, acid arrow, and Web, they'd be very annoying to PCs that might engage our boss here with ranged weapons. That said, GM Arkwright's suggestion is also excellent. Perhaps lesser versions with only two mythic ranks?...
Thanks for the crits, folks, keep it coming! The more data I have, the better this is going to turn out.
I'd definitely fight this thing. I don't think it's OP at all, assuming they have the right gear for it. As Redjack said, it might even need more health. If they gang up on it and start smacking it, it wouldn't surprise me if they killed it in two rounds. If they use ranged weapons, they can avoid the rune of agony and not have to wait a round to full attack, which could be really bad for this thing.
It's got a lot of cool stuff, but it's not doing anything crazy. The rune of terror and shockwave are pretty nasty though, I think it's a really cool monster.
The level 12 non-mythic Hunter archer in my current party could kill this thing herself in two turns. 30 AC with only 160 HP is going to be very short work.
If you have a full BAB guy who intelligently took Mythic Vital Strike with his mythic feat, he'll be looking at, probably +22ish? to hit, and he'll be attacking three times per round (normal standard, mythic power for a bonus standard, swift action to use a champion/trickster bonus attack thingy) for something like 4d6+50 or so damage each. Those save DCs are really low (DC 17? Really?), so, I don't think things are looking so good for your construct.
I use mythic to help compensate for the PC power creep that happens late-game; putting a few ranks on boss monster-type encounters is starting to become SOP. It's not so much a house rule as a comment on how I look at things, but: in my games, mythic ranks are not a good indication of how well-known something is. Especially if it's been guarding the deepest room of a dungeon for...hundreds of years, at this point. Meanwhile the civilization that built it has crumbled around it (which happens to be exactly the case).
What if the presence of other ancient constructs scattered about the ruins- some potentially helpful, some not- served as a clue? Seeing smaller versions of this thing scattered around would get me prepping to fight one f I were a PC. Plus a few bits and pieces of lore scattered around (if the ancient civilization was proud of their work, they might write about it somewhere the PCs can find it)? It's not exactly a cold open, but I don't really want to give them anything so concrete as, "It's a big construct. Don't forget the adamantine ammunition and bludgeoning weapons."