#3 (Tie) - Delsenora (1st Edition chase, 10/25)
Upon further review, we have a tie at #3. Delsenora's ability to cancel an event as she is discarded is so powerful that she simply has to be on this top 3 list. Delsenora's effect can be a literal game-changer. She can stop an opponent's Caer Allison, Caravan, or Good Fortune, potentially crippling their hand or stopping a game-winning play. She can also safeguard your own interests by stopping an enemy Calm, Cataclysm, or Ambush. Events are so powerful (and important) in this game that any card able to mess with them has to be respected and planned for. Just having Delsenora in your pool can make other players wary and nervous about playing events. Their hesitation is your gain!
#3 (Tie) - Shayira (4th Edition, 286/500)
Just edging out Tyvorg, Ting Ling, and a few others we have Shayira, whom I have already written about here. The ability to ignore the special powers of all cards played against her in combat is just primo. She can't be killed by cheese, so must either be nuked in her pool by cards like Finger of Death and Drain Will, or beat in a level-up war. The downside to Shayira is her low level. Ordinarily, a level 3 champion is great for getting your own instant-kill cards off before your opponent does, but since Shayira is immune to them anyway a higher level would have made her even better. Oh, well. She's still good enough to take #3 on this list.
#2 - Goldmoon (Artifacts, 83/100)
Now this is a powerhouse champion! Once per turn, at any time, she can grab a cleric spell from an opponent's discard pile and cast it. What an awesome ability! So, your enemy is pleased with himself after casting that Mindshatter, Creeping Doom, or Mindkiller? Wait until Goldmoon grabs it and beats him over the head with it. In a multi-player game, this champion is even better. Each turn there is likely to be a card to take out of an opponent's graveyard and cast. Another great use of Goldmoon is to wait until someone casts something you don't like, then instantly grab a Dispel from a player's discard pile. If it's an event you don't like, check around for an Intercession! See how great this champion is? Be warned, however, that Goldmoon has no immunities and attracts champion-killing cards like a magnet.
#1 - The Arch-Druid (4th Edition, 285/500)