Can my players' plan to raise the Tarrasque with animate dead work?

Question

This is the first game I have GMed and this game has been going on for some time (with house rules to allow progression past lv20). The players have now figured out that they will eventually face the mighty Tarrasque. One of the players (a necromancer) has let slip an ingenious plan to defeat the beast and I am unsure how to deal with that when it comes up.

The wizard in question plans to use a 750gp onyx and the animate dead spell to raise and control the 30HD Tarrasque. This is supposed to be an unstoppable beast but as far as I can tell all they need to do is smack it hard enough and then they control a Zombie Tarrasque. At 4HD per CL the Necromance is more than able to control a 30HD beast.

But, how does that play out against the regenerate ability?

Regeneration (Ex) No form of attack can suppress the tarrasque's regeneration—it regenerates even if disintegrated or slain by a death effect. If the tarrasque fails a save against an effect that would kill it instantly, it rises from death 3 rounds later with 1 hit point if no further damage is inflicted upon its remains. It can be banished or otherwise transported as a means to save a region, but the method to truly kill it has yet to be discovered.

As far as I can tell I only have a few options as GM:

1. Congratulations, you now own a Zombie Tarrasque, for home work you can stat that thing up.
2. The zombie drops HP at the rate of 40 a round, until you run out of repair undead, it dies, and then the tarrasque comes back.
3. Not bring the beast into play at all (not a great option).

Help.

Answer 1

As GM, you always have more options than you think, and you should always try to choose the one that's the most fun. My vote would be for the following:

4. This infuses the tarrasque with negative energy, creating an eldritch horror that threatens all of existence.

The rules don't say exactly where the tarrasque came from or how it works, but it's safe to assume that the creature is powered by some unlimited source of magic energy deep within its hulking form. The animate dead spell will corrupt this power source with negative energy, creating a threat to existence itself.

The most immediate effect will be the creation of an undead creature much more powerful than the original tarrasque, and certainly not under the control of the PC necromancer. The power of this creature will only grow over time as its power source becomes more corrupt. The creature will emit a negative energy aura that extends for miles, granting many permanent negative levels to creatures who fail their save and transforming most living creatures in the area to undead. As the creature's power grows, nightshades will begin to come forth from the negative energy plane to join with it, and it will begin to emit waves of negative energy of increasing radius. All natural healing of living creatures will cease, the dead will begin to rise from their graves, and material plane will begin to merge with the plane of negative energy.

It's up to the PCs to find out where the original tarrasque came from and how they can undo the damage that they have done. They might also have to deal with powerful planar beings who would use the abomination for their own ends, or who hope to defend the multiverse from the threat now posed by the material plane.

Answer 2

RAW, this method of defeating a tarasque generally will not work, but some exceptions may exist.

The target of the Animate Dead spell is a corpse.

This spell turns corpses into undead skeletons or zombies that obey your spoken commands.

Corpse means dead body. In 3.5 the text of the spell is even more straightforward

This spell turns the bones or bodies of dead creatures into undead skeletons or zombies that follow your spoken commands.

Pathfinder lacks this level of detail, but still talks about corpses.

At the same time the description of the Regeneration special ability reads:

Creatures with regeneration heal damage at a fixed rate, as with fast healing, but they cannot die as long as their regeneration is still functioning (although creatures with regeneration still fall unconscious when their hit points are below 0).

So you can't defeat tarasque by Animate Dead spell. You need to kill it somehow before you use Animate Dead on it.

If you do kill it and use the spell, then the created undead wouldn't have regeneration ability, because both zombies and skeletons loose it when created.

A zombie loses most special qualities of the base creature. It retains any extraordinary special qualities that improve its melee or ranged attacks.

and

A skeleton loses most special qualities of the base creature. It retains any extraordinary special qualities that improve its melee or ranged attacks.

Regeneration doesn't improve attack, so it is lost.

So generally, you can't kill tarasque that way. The only thing that remains undisclosed is the specific wording of the tarasque regeneration ability that states

If the tarrasque fails a save against an effect that would kill it instantly, it rises from death 3 rounds later with 1 hit point if no further damage is inflicted upon its remains.

The general rule is: “Specific overrides general”. If we take the quote above literally, then tarasque will be effectively dead for 3 rounds until its regeneration ability will bring it back to life and thus a valid target for animate dead spell during that time. And after animating it will lose its regeneration ability. Remember, you need an instant kill, reducing tarasque below 0 hp wouldn't work.

But I'd advise a great caution about this exploit. Tarasque CR is that high because it is virtually indestructible. Allowing a comparatively low-level spell to override it can be unbalancing.

(all emphasis mine)

Answer 3

Check out the descriptions in the Bestiary:

'If the creature has more than 20 Hit Dice, it can't be made into a skeleton by the animate dead spell.'

Zombie is more wonky, but you could argue that its 30+x (x=10?) HD are not covered by the chart and therefore such a zombie is impossible.

Answer 4

Firstly, Animate Dead has a target of "one or more corpses touched", so the Tarrasque need to be dead (like, for real, not just below 0 hp and regenerating), and there is no way to do that by simply following the rules and the canonical universe (RAW there is ambiguous cases where you could consider that the Tarrasque should be dead, but it's no way as simple as "smacking it hard enough"). So let's assume in your universe you decided that there is a way to really kill the Tarrasque, your group did it, and your necromancer is raising it.

Secondly, Animate Dead can create only Zombies or Skeletons, and :

A skeleton loses the base creature's defensive abilities and gains DR 5/bludgeoning and immunity to cold. It also gains all of the standard immunities and traits possessed by undead creatures.

Zombies lose their defensive abilities and gain all of the qualities and immunities granted by the undead type. Zombies gain DR 5/slashing.

So the Zombie Tarrasque will loose its regeneration, and get instead a crappy DR 5/slashing.

Thirdly, let's assume your player raised a Zombie and somehow make it gain regeneration. The regeneration would work as normal, making it gain hp each turn. Regeneration is not a positive energy effect.

Answer 5

Why not require a Wish?

The Pathfinder reference document's entry on the Tarrasque comments that

the method to truly kill it has yet to be discovered.

Drawing some inspiration from D&D 5e's Tarrasque, you could require that some unique quality of the Tarrasque requires a Wish in order to kill it, and another Wish in order to raise it as an undead. Doing this bypasses the RAW issues with Animate Dead, and allows your players to raise the Tarrasque as their own undead while giving you the freedom to limit the power of their new pet, under the "partial fulfillment" part of the spell. For example, you could rule that an undead Tarrasque no longer has the vitality for its regeneration ability.

Depending on how you want to play it, you could either tell your players that they need to use a Wish, or you could just let the Animate Dead fail in a way that suggests a stronger spell is needed.