Who pays the XP cost for a spell the Eidolon casts?

Question

The epic spell Eidolon creates a magical duplicate of the caster, "fully rested" and with all the spellcasting potential of its level.

Including the ability to cast spells with a XP cost.

Who pays the XP cost for the eidolon spells?

Answer 1

This took a bit of discussion and looking up the original in the Epic Level Handbook to parse, but here's the consensus.

You pay the xp cost.

The SRD, while great in other ways, doesn't include an example of the spell in use, as the Handbook does. In the exaple, a 30th level wizard creates a 21st level eidolon, then feeds him more levels until he's effectively 26th level and the eidolon is 25th level. At the end of the spell, those levels return to the wizard.

That, plus the seeds and factors, makes clear that you are effectively creating a body that looks like yours, then powering it with your levels. As a result, the body has your powers and thoughts (to a lesser extent, it's only part of you) but is otherwise it's own entity- you've effectively made a temporary cohort of yourself.

This means that when an eidolon casts a spell with an experience cost and pays that cost, it's coming out of part of your soul- when the eidolon returns those levels to you, it'll be without the experience burned casting an epic spell.

This has some, ah, possibly unintended implications. If it's part of you, the eidolon could conceivably earn experience just as you could, and return with more experience than it spent. Used this way, the wizard from the example could send a 25th level version of himself adventuring in his place, reaping the rewards and only risking 2500 xp per casting.

One final note- nowhere is it even implied when you pay the experience cost of a spell cast by the eidolon. Per this interpretation, you would pay the cost (and gain the experience earned, if any) when the eidolon died or the spell ended, whichever came first... though the thought that an eidolon could cast epic spells one after the other, allowing you to postpone the xp cost for up to 8 hours, is potentially game-wrecking.