Two cards go in. Something that has never existed comes out.
Spend your turn and two of your monsters to merge them: new name, new art, new stats, effects inherited from its parents. It lasts one duel — the discovery is what you keep.
Three lanes a side, one card per turn. Monsters carry their wounds between turns, and damage past a defender spills onto the player behind it.
Several duelists, each one stronger than the previous!
Card battler where you merge two cards into a monster that has never existed.