It is almost always better to use them for Level 2 Synchro, Rank 1 Xyz, or any Link strategies
One of the things we had talked about but didn't want to do in normal sets were cards that acknowledged gameplay with more than two players
Now, you can use consistency, protection, and/or interaction cards as your field spells
If a creature card that was exiled is no longer in exile when Kaya, Spirits' Justice's first ability resolves (perhaps because of Pull from Eternity or a similar effect), you can't choose that creature card with that ability
The return of the Poison Counters in Phyrexia: All Will Be One has been contentious, especially in the Commander format
Of course, thats why rare cards are always worth chasing down