msem-instigator

Put a +1/+1 counter on each of up to X target creatures.
Augmented — If you've spent {W}{U}{B}{R}{G} to cast spells this turn, instead put three +1/+1 counters on each of those creatures. They gain trample until end of turn.

{T}: Add one mana of any color a basic land you control could produce.

Enchant creature
Enchanted creature gets +2/+2 and has lifelink.

When Biohazard enters, destroy all other nonland permanents with mana value X or less.
At the beginning of each end step, each opponent loses life equal to the number of cards they've drawn this turn plus the number of spells they've cast this turn.

Return up to one target spell to its owner's hand.
Create two 1/1 blue Elemental creature tokens with flying. They can't block this turn.

When Bioluminescent Predator dies, draw a card, then you may put a land card from your hand onto the battlefield.

When Bird Call enters, search your library for a creature card, reveal it, shuffle, then put that card on top.
{2}, {T}: Target creature gets +1/+1 until end of turn.

Lifelink
At the beginning of your end step, if you've gained 3 or more life this turn, create a 2/2 white Bird creature token with flying.

Flying
Bird of Many Feathers can block only creatures with flying.
Whenever you scry, put a +1/+1 counter on Bird of Many Feathers.

Create a 1/1 blue Bird creature token with flying, then put the bottom card of your library into your hand.

Exchange control of two target permanents that share a permanent type.
Lifecycle {3} ({3}, Discard this card: Create two tapped 1/1 colorless Elemental creature tokens.)

Create a 1/1 blue Bird creature token with flying. (Cast a copy of this spell once while this creature is on the battlefield.)

All creatures get -4/-4 until end of turn.

Legacy (You may play this side of this card only from your graveyard. Exile it if it would leave the battlefield or not resolve.)
Permanents you control have lifelink and “{T}: Add one mana of any color.”

Whenever a creature card is put into your graveyard from the battlefield, exile it. You lose life equal to that card's mana value. Put it onto the battlefield tapped at the beginning of your next upkeep.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
Return target creature card from your graveyard to the battlefield. If it was put there from the battlefield this turn, create a token that's a copy of it. If you're in a renaissance, create a token that's a copy of it.

Whenever Birthing Elemental or another nontoken creature you control dies, create a 1/1 green Saproling creature token.

Menace
When Bit Player dies, it deals 1 damage to each opponent.

Destroy target creature with flying.

At the beginning of your end step, mill two cards. Then if ten or more cards are in your graveyard, transform Bitter Duckling.

This spell can't be countered.
Whenever Bitter Leviathan becomes the target of a spell or ability, exile it. Return it to the battlefield under your control tapped and attacking at the beginning of the declare attackers step on your next turn. It can't be blocked that combat.

Target player discards a card. Return a creature card from your graveyard to your hand.

When Bitter Pact enters, destroy target nonbasic permanent.
All permanents and players lose hexproof, indestructible, and protection and can't have or gain hexproof, indestructible, or protection.

Target opponent reveals their hand. You choose an instant or sorcery card from it or a card from their graveyard. Exile that card.

Return to your hand all permanent cards in your graveyard that were put there from the battlefield this turn.