msem-instigator

Whenever Babbling Experiment or another creature enters the battlefield under your control, target player mills two cards.

When Babyscale Bruiser enters the battlefield, you may reveal a creature card from your hand. If you do, Babyscale Bruiser deals damage to target creature an opponent controls equal to the revealed card's power. That creature deals damage equal to its power to Babyscale Bruiser.

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.

Desecrate (When this creature enters the battlefield, you may sacrifice an artifact or land.)
When Back-Alley Vandal desecrates a permanent, put a +1/+1 counter on Back-Alley Vandal.

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.

Deathtouch
When Backstage Comic enters the battlefield, target player discards a card.

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

When Backstage Tinkers enters the battlefield, you may return an artifact card from your graveyard to your hand.

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

Menace, haste

(Transcend as a sorcery to gain that 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.

Menace
As long as Balefire Harbinger is attacking, creatures in its pack can't be blocked unless defending player pays {1} and 1 life for each creature they control that's blocking one of those creatures. (Two or more creatures you control with equal power are in a pack.)

This spell costs {U} less to cast if you dealt combat damage to a player this turn with a Rogue.
Flying
When Balloon Voyager enters the battlefield, draw a card.

At the beginning of combat on your turn, if there are five or more creature types among creatures you control, creatures you control get +2/+0 and gain menace until end of turn.

Whenever equipped creature attacks, it gains deathtouch until end of turn.
Sacrifice Bandit's Dagger: Target player dealt damage by equipped creature this turn reveals their hand. You choose a nonland card from it. That player discards that card.
Equip {2}

Engorge (As this enters the battlefield, mill three cards, then exile a card from among the milled cards.)
When Bane of Sanity enters the battlefield, if it engorged a creature card, target player discards two cards.

Haste
Whenever Banished Companion attacks, it deals 2 damage to you.

Exile up to three target cards from graveyards. (Then exile this card. You may cast the creature later from exile.)

When Banishing Initiate enters the battlefield, you may exile target nonland permanent you don't control until Banishing Initiate leaves the battlefield.
At the beginning of your end step, sacrifice Banishing Initiate if a card exiled with it has mana value 3 or greater.

Lifelink
{1}, Discard Bant Shardseeker: Search your library for a basic Island or Forest card, reveal it, put it into your hand, then shuffle.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
Baptism by Fire deals 3 damage to target creature or planeswalker. If you're in a renaissance, Baptism by Fire deals 6 damage to that permanent instead.

Vigilance
{1}{W}: Barbarian Axe Flinger gains double strike until end of turn.

When Barbarian Intimidator enters the battlefield, target creature can't block this turn.
When Barbarian Intimidator enters the battlefield, prevent all combat damage that would be dealt to target creature this turn.

Other Warriors you control have first strike.
Other Barbarians you control get +1/+0.

Battalion — Whenever Barbaric Ambusher and at least two other creatures attack, you may tap target creature.