I'm back at it with some silly ideas.
LEVEL -1 - OLD AMBER
CRETACEOUS BARK: All cards of higher Level than this lose 1 Level.
(CLEVER GIRL): This card knows the answer to any math operations that need to be performed. Can't speak though.
As a negative level card, it should be instantly discarded, and how is amber supposed to bark anyways? Well, that's with a little help from...
LEVEL 3 - NECROMANCER
(UNDEAD): This card is undead.
CHECK THIS OUT: Choose a card from your discard pile. Play that card, which now has a Level equal to half of this card's Level (rounded down). That card also has the (UNDEAD) passive now.
A way to introduce more undead into the game, possibly make zombies even stronger than their living selves. The key is the necromancer's skill, not the ingredients!
LEVEL 2 - SPIRAL DOMAIN
TWISTING REALM: All players count the cards in their hands, then put them all in a neat pile. Shuffle the pile and give out the same amount of cards they had to each player.
(UNREAL DOOZY): At the start of your turns, everyone draws their card from the player to their right's deck, instead of theirs.
This card only works if you are playing in such a way that makes deck mixing not a hassle, such as if you are playing with a single deck (in which case its passive is useless). I always think all-player-shuffles are fun, though!
LEVEL 2 - SELF-HELP BOOK
(VISUALIZE YOUR LIFE): Undead cards you control gain 1 Level.
(VISUALIZE YOUR DEATH): This card takes a maximum of 1 damage when attacked by a card that isn't undead.
Another addition to the undead theme, some needed guidance for those poor souls!
LEVEL 1 - BATRACHIAN
(NICE AND FRESH): If it's currently raining, this card gains 2 Levels.
LONG TONGUE: Deal lethal damage to a Bug.
(CROAK): When this card is defeated, give whoever is responsible a long and disapproving look.
Simple card, also good against specific opponents (unintentionally building some "type effectiveness" kind of rap). I wanted to draw a funny frog tongue.
LEVEL 3 - BABY CHILD
(HELLO WORLD): When Baby Child is first played, choose two cards. Baby Child inherits a Passive from one of them, and an Action from the other. Those cards are considered Baby Child's parents, and cannot harm Baby Child in any way, unless Baby Child defeats another card, at which point they see the monster they've brought upon this world.
I really like making this sort of """modular""" cards that allow for lots of possible combos and synergies.