msem-instigator

When Azure Archaeologist enters, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
{2}, {T}, Sacrifice a Clue: Draw two cards, then discard a card.

Flying, trample
Prismatic — Whenever you cast a multicolored spell, put a +1/+1 counter on Azure Caterwauler.

Draw X cards, where X is the number of differently named lands you control.

When Azutahn Hydromancer enters, you may return target creature with power X or less to its owner's hand, where X is the number of differently named lands you control.

Whenever Babbling Experiment or another creature you control enters, target player mills two cards.

Put two +1/+1 counters on target creature. Untap that creature.

First strike
Back-Alley Gnoll has lifelink as long as it's enchanted by a black Aura.
Back-Alley Gnoll gets +2/+0 as long as it's enchanted by a red Aura.

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever Backalley Silencer deals combat damage to a player, destroy target marked creature.

Haste
When Backdrop Artisan dies, audition for red. (Create a 1/1 Construct Actor creature token, a Warrior Role giving 3/2 and trample, or a Wizard Role giving 2/2 and prowess. Roles replace older ones.)

Backstabbing Courtiers can't attack unless you foretold a card or cast a foretold spell this turn.

Non-Actor creatures can't block this turn.

When Backstage Broken enters, create a 1/1 colorless Construct Actor creature token.
Whenever a token you control leaves the battlefield, you gain 1 life.

Lifelink
At the beginning of your end step, if you gained life this turn, put a +1/+1 counter on Backstage Manager.

At the beginning of your end step, create a 1/1 white Soldier creature token.

Basic Forests you control have “{G}, {T}: Untap target attacking creature and remove it from combat.”

Exile target creature or planeswalker. You gain 4 life.

Flying
{B/G}, Discard a creature card: Badru, the Skyshadow becomes a copy of the discarded card until end of turn, except he has flying and is 5/5.

Destroy target creature. Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

{W}{B}{G}, Discard a card named Bahet, God of Destruction: Bahet gains indestructible and becomes a God creature in addition to its other types.
Whenever Bahet enters or attacks, each player chooses a number of lands they control equal to the number of lands controlled by the player who controls the fewest, then sacrifices the rest. Players discard cards and sacrifice non-God creatures the same way.

As an additional cost to cast this spell, discard your hand.
Purge four times, then you gain 1 life for each card in exile. (Exile two cards that share a type from graveyards. If you do, draw a card.)

[+1]: Discard a card. If you do, up to one target player gains 5 life.
[–3]: Discard a card. You draw X cards and you lose X life, where X is that card's mana value.
[–7]: Exile your hand, then put all cards from your graveyard into your hand and all cards exiled this way into your graveyard.

[+1]: Exile up to two target cards from graveyards. You gain 3 life.
[–2]: Exile target artifact, enchantment, or nonbasic land.
[–7]: You get an emblem with “At the beginning of your upkeep, exile target noncreature permanent.”

Transcend (Activate as a sorcery to gain the next type and a +1/+1 counter.)
Flying
{1}{W}: Demigod — Return up to one target creature card with mana value 2 or less from your graveyard to the battlefield.
{3}{W}: God — Put a +1/+1 counter on each creature you control with the least power among creatures you control.

When Bal's Descent enters, each player sacrifices a creature, discards two cards, and mills three cards.
{1}{B}{B}: Transform Bal's Descent. Activate only if your fealty to Swamps is five or greater.

Prowess
Whenever Balefire Conjurer attacks, you may pay {1}{R}. If you do, exile the top card of your library. You may play that card until the end of your next turn.