msem-instigator

Flash
Once each turn, you may cast a spell without paying its mana cost. If you do, at the beginning of your next upkeep, you lose the game unless you pay that spell's mana cost.

Flying, first strike, vigilance, lifelink
When Bastion Valkyrie dies, create three Function tokens with “Choose a creature targeted by this spell. It gains flying, first strike, vigilance, and lifelink until end of turn.” (They're enchantments. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
Battering Swine attacks each combat if able.

When Battery Courier dies, lose 2 life.

{4}{G}: Battle Station gets +3/+3 until end of turn.
Cycling {2/G} ({2/G}, Discard this card: Draw a card.)

Flying, lifelink

When Bauble Collector enters, you may return another permanent you control to its owner's hand.

Concord — When Bazaar Equestrian enters, if there are four or more card types among permanents you control, you gain 4 life.

Beachhead Partisan has first strike as long as it's attacking.
When Beachhead Partisan enters, it deals X damage to any target, where X is the number of tapped creatures you control.

Whenever you detain a permanent, you gain life equal to that permanent's mana value.

Auras and Equipment you control have indestructible.
Whenever Bearidge Marshall attacks, you may create a white Aura enchantment token named Arrest attached to target creature. It has enchant creature and “Enchanted creature can't attack or block, and its activated abilities can't be activated.”

Whenever you cast an instant or sorcery spell, each opponent loses 1 life and Beast of Pestilence gets +1/+1 until end of turn.

Menace
When Beatrice enters, target opponent reveals their hand. Exile a nonland card from it. During any turn that player lost life, you may cast that card and mana of any type can be spent to cast that spell.

Whenever you cast an enchantment spell, you draw a card and you lose 1 life.
Whenever one or more counters are put on an enchantment you control, you gain 1 life and each opponent loses 1 life.

Concord — When Beetleback Forager enters, if there are four or more card types among permanents you control, return target card from your graveyard to your hand.

Trample
Whenever Belligerent's Augur or another Warrior you control deals combat damage to a player, you may pay {1}{U}. If you do, draw a card.

Whenever Beragnian Brawlmaster or another Warrior you control enters, that Warrior fights target creature an opponent controls.
{R}{W}: Target Warrior creature gets +1/+1 until end of turn.

When Bessie's Brood enters, it fights target creature. (If there are no other creatures, it eats itself.)

Deathtouch
When Bitterheart Bokor leaves the battlefield, you may search your library for a Curse card, reveal it, put it into your hand, then shuffle.

When Bjarndyr Mender enters, other creatures you control get +1/+1 and gain indestructible until end of turn.

Flying
When Blackblood Feaster enters, you may have each player sacrifice a creature.
Pay 2 life: Blackblood Feaster gets +2/+2 until end of turn. Activate only once each turn.

Flying, lifelink
Whenever Blackhearted Sphinx attacks, you may pay 3 life. If you do, draw a card.

At the beginning of combat on each of your turns, look at the top card of your library. You may put that card into your graveyard.
Whenever a land card is put into your graveyard from anywhere, each opponent loses 1 life and you gain 1 life.

Flash
When Blade of Mautakesh enters, creatures you control gain poisonous 1 until end of turn. (Whenever those creatures deal combat damage to a player, that player gets a poison counter. Multiple instances of poisonous trigger separately.)

Flying
Whenever Blade of Reckoning deals combat damage to a player, that player sacrifices an untapped permanent.