Dawn of the Mindflayers
Rules: the main point is to lobotomize creatures with mindflayers. If a mindflayer of yours lobotomizes a creature with a skill, you get +1 point (even if it was your own creature).
Each mindflayer in the deck also gives +1 point. This encourages players to pack 6 of them in their deck, but there is only 1 deckbuilding rule:
Fractal and Mitosis are banned. Anything other is permitted. Note that lobotomizing with Lobotomizer doesn't give points.
We will duel three times, no matter who wins and loses. If a player wins a match, he gets +3 points.
The winner of the challenge will be the one who has more points.

Edit: didn't mention but upgraded cards are allowed, but not necessary.