msem-instigator

Flash
When Augmented Spawn enters the battlefield, create a 1/1 blue Merfolk creature token for each Island you control.
{U}, Sacrifice a Merfolk: Augmented Spawn gains hexproof until end of turn.

Trample
When Bank Skimmer enters the battlefield, create a green Aura enchantment token named Turtle's Valor attached to target creature. The token has enchant creature and “Enchanted creature gets +X/+X, where X is its mana value.”

Defender
Discard a card: Barge Engulfer can attack as though it didn't have defender until end of turn.

Vanguard — Whenever a creature you control attacks alone, it gets +1/+3 until end of turn.

Vigilance
Whenever Bartimus attacks, another target attacking creature gets +1/+1 until end of turn. If that creature is a Soldier, put a +1/+1 counter on it instead.

When Benthic Alchemist enters, draw a card, then discard a card, then mill a card.
Whenever you cast an instant or sorcery spell, create a 1/1 colorless Elemental creature token. It gains haste until end of turn.

{T}: Until end of turn, target land is every basic land type in addition to its other types and its name becomes Morphic Sea.

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.

({T}: Add {U}, {B}, or {R}.)
Bleak Dominion enters the battlefield tapped.

Whenever you discard a card or an artifact is put into your graveyard from the battlefield, put a +1/+1 counter on Bloodhollow Bruiser.
Cycling {2} ({2}, Discard this card: Draw a card.)

Flash (You may cast this spell any time you could cast an instant.)
When Bloodhunter Orca enters the battlefield, target opponent sacrifices a creature that was dealt damage this turn.

({T}: Add {U} or {R}.)
Boiling Ridge enters the battlefield tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Sacrifice Bonetooth Darter: Counter target instant, planeswalker, or sorcery spell unless its controller pays {1}.

{1}, Sacrifice Brackwater Scuttler: Draw a card.

When Braenid Nomad enters the battlefield, draw two cards, then discard a card.

{1}{G}: Target land you control becomes a 3/3 green Elemental creature until end of turn.
{1}{U}: Target enchantment you control becomes a 2/2 blue Nymph creature with flying until end of turn.

When Bridled Narwhal enters the battlefield, you gain 5 life.

Defender
When Brine Duelist enters the battlefield, create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)
{W}{U}{B}{R}{G}: Put a +1/+1 counter on Brine Duelist. It loses defender.

Whenever you draw a card, you may have target player mill two cards.

When Broadside Raider enters the battlefield, create a 1/1 blue and red Pirate creature token with haste.

This spell costs {1} less to cast for each artifact and/or enchantment you control.

{6}{U}: Brume Trench-Thrasher can't be blocked this turn. This ability costs {1} less to activate for each instant and sorcery card you own in exile and in your graveyard.

Concord — Whenever Bubbledome Captain attacks, if there are four or more card types among permanents you control, each other attacking creature gets +1/+1 until end of turn.

When Bubbledome Chorister enters the battlefield, create a green Aura enchantment token named Sanctum's Gift attached to target creature. The token has enchant creature and “Enchanted creature has ‘{T}: Add {G} for each enchanted creature you control.'”

Whenever you cast an enchantment, instant, or sorcery spell, create a 1/1 blue Jellyfish enchantment creature token with slipstream. (It can't be blocked as long as only creatures with slipstream are attacking.)