Tips for beating a Tarrasque?

Not with plain shift and you won't be able to kill him on your own. You'd have to be able to cast Disintegrate and Wish in the same round. You would need the feats Epic Spellcasting and Multispell in order to kill him in one round. He regens all damage every round, since he has 40 HP regen, and Nothing does lethal damage to him. The only other way I can see would be using an effect that would cut off his air, or drown him til he was helpless then using wish to kill him.