Even late game, Undo could take out two key blockers allowing for your creatures to swing in for that last few damage
We all know how good these kinds of cards are and I am sure I have written at length about them with not much having changed in regard to such cards since then
Still, a lot of cards were left out before the invention of this new, acorn technology
The other 60% of the time, its a 3/3 with scry 1, and we should not be in the market for that
You choose a target for that ability as it goes on the stack
Use Auras to keep your Pearl-Ear, Imperial Advisor and other value creatures protected so that your engine sticks around, cast a lot of enchantment creatures to widen the field for cheap, and then drop haymakers, like True Conviction, Legion Loyalty, Cathars Crusade, and Boon of the Spirit Realm, to go for the kill