You could do unfair things with Eradicate
Ancestral Vision Its pretty easy to see why Ancestral Vision is a strong card, as its a fixed version of Power Nine Ancestral Recall
14 sources will give you an 86 percent chance of having one in your opening hand
The right play is going to depend on the matchup (if they're a very fast deck it could be right to block), your hand (if your next play is a Ghoulraiser and your creature is instead a Walking Corpse, it is excellent to block), and your tribe along with your deck
Look, all concessions to you people who play Titania, Protector of Argoth and say, But but but but you also create three 5/3 creatures! Im going to say, Okay, and for all those times you didnt have Titania on the battlefield? Horrible city
The flip condition seems fair: play two Spirits or Arcanes, collect two ki counters, then flip