I think I'm missing a rules subtlety somewhere - why does losing the new Thassa cause evolve to work, but losing the old doesn't? In either case, the Thassa isn't a creature when evolve resoles (unless AP has another permanent for his devotion?).

EDIT: Wait, I think I got it - Thassa was briefly a creature, which triggered Evolve. Then if the new one is put into the graveyard, when evolve resolves you use last known information about the Thassa that died to get the P/T. On the other hand, if the old Thassa was the one that died, then this Thassa becomes a non-creature which makes evolve fail. Is this correct?

Edited Talia Parkinson (March 26, 2014 09:29:49 AM)

Yes, that's correct.

If he bins the new Thassa, then when the Evolve trigger starts to resolve the referenced permanent isn't around anymore, so we need to use last-known information to determine its characteristics. When it was last on the battlefield, it was indeed a creature (he had 5 devotion) with sufficient power or toughness, and so the evolve trigger will resolve.

On the other hand, if the old Thassa gets binned, then when the Evolve trigger starts to resolve the referenced permanent is still on the battlefield, but it isn't a creature anymore, so the intervening-if of evolve fails: the power and toughness on Thassa are undefined, so they are treated as 0.

Edited Vincent Roscioli (March 26, 2014 09:33:40 AM)

Thanks Vincent.

This being the case, I find myself agreeing with Josh's recommendation of asking AP which Thassa he chose to have die, and in the case that he genuinely can't recall, go with NAP's choice. I don't think saying “I intended to have my raptors evolve” is showing enough rules knowledge, especially if the AP can't respond to me by properly determining which Thassa needed to die for this trick to work out as intended. This is a pretty subtle trick, so demonstrating awareness of how that subtlety plays out is key.