Th champion is fine. You could make it neutral to allow other decks to make better use of the card, or you could say “when one dies, the other becomes a champion” instead of “if one kills the other”. That way you have the advantage of interacting first. Or you could say the teo cards pulled dont take damage from anything but the other card.
I feel like making it neutral is the best Idea. (Cough pulls spec rev cough)
The problem isnt the mana or the champion. The problem is its a card that basically says " put your opponent ahead"