Challenges sees two players comparing the strength and health of the attackers chosen card/s and the targeted card/s, with the two exchanging the amounts
This character sings for six, and since he only costs four ink to play, gives you a huge jump ahead in value
The war may be the same, but the battlefield is always new with Commanders Inquisitor Greyfax and Marneus Calgar. For a typical Magic design, I would have expected Celestine, the Living Saint to be yet another powerful legendary Angel, so I appreciate having it as a Human Warrior instead
You choose the target for that ability at that time
For example, if an effect has given Nylea's Colossus -8/-0 so that it's a -2/6 creature, doubling its power and toughness gives it -2/+6, and it will become a -4/12 until end of turn
Plus, with Bloodline Necromancer, you can simply reanimate all of the creatures that you sacrifice to Disciple of Bolas