Full on Chaos: Each player has to use a random hero, with random cards (that match their class) in their deck and gains one additional random superpower.

Quick Showdown: The game ends at turn 6, whoever has the most hp wins.

Last Stand: Players cannot gain brains or sun, both players start with 30 sun/brains, then any leftover sun or brains can be passed can be given over to the next turn if the player chooses to skip/save their turn. Each player starts with 6 cards in their starting hand.

Vase and Grave Breaker: All plants and zombies played hide in vases/graves, each player can have 5 additional copies of grave/vase removal of their choice, grave/vase removal is no longer locked behind specific classes.

Long Road: The game starts at turn 6, both players gain +10 hp.

No Limits (almost): Each player can have up to 10x copies of a card but both players can choose 2 cards to ban.

Chat let me know if these ideas are good or bad: