(Edited to incorporate Peebs' suggestions)
Sir Bedevere--$4
Action-Attack-Reaction-Knight
Each other player reveals the top 2 cards of his deck, trashes one of them costing from $3 to $6, and discards the rest. If a Knight is trashed by this, trash this card.
--
When another player plays a Witch, you may reveal this from your hand. If you do, measure that player's weight against the weight of a duck. If they weigh the same, you are unaffected by the attack, that player trashes the Witch, then you may burn that player at the stake.
***
Sir Robin--$3
Action-Attack-Reaction-Knight
Each other player reveals the top 2 cards of his deck, trashes one of them costing from $1 to $3, and discards the rest. If a Knight is trashed by this, trash this card.
--
If Sir Robin is revealed for any reason, discard it immediately.
***
Sir Not-Appearing-in-this-Film--$5*
Action-Attack-Knight
Each other player reveals the top 2 cards of his deck, trashes one of them costing from $3 to $6, and discards the rest. If a Knight is trashed by this, trash this card.
(This is not in the Supply.)