msem-instigator

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.

Vision (Whenever this or another creature you control enters, reveal the top card of your library. Then you may put that card into your graveyard.)
Whenever Blind Soulcaller envisions an instant or sorcery card, you may tap target permanent.

Prowess

Engorge (As this enters, mill three cards, then exile a card from among the milled cards.)
When Bloodchill Risen enters, if it engorged an instant card, return target creature to its owner's hand.

Flying
When Blossoming Hatchling enters, create a Treasure token.

Dominance — If you control the creature with the greatest power or tied for the greatest power, you may pay {U} rather than pay this spell's mana cost.
Counter target spell unless its controller pays {3}.

Flying, prowess

Prevent all combat damage that would be dealt to and dealt by creatures this turn.

You may have Blurry Counterpart enter as a copy of any creature on the battlefield.
Mirage {1}{U} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

Flying
When Bogsnatcher Drake enters, create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature doesn't untap during its controller's untap step.

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}.

When Boneweary Warrior dies, you may put a -1/-1 counter on target creature.

Return target nonland permanent you control and target nonland permanent you don't control to their owners' hands.

Whenever a creature you control deals combat damage to a player, you may sacrifice it. If you do, draw cards equal to that creature's power.

Whenever Bound Apparition becomes the target of a spell or ability, put a -1/-1 counter on it.

You may cast a spell with mana value 3 or less from your hand without paying its mana cost. (Then exile this card. You may cast the creature later from exile.)

Flying
Whenever you attack, another target creature you control gains flying until end of turn.
Fleeting {U} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

Enchant creature
Enchanted creature doesn't untap during its controller's untap step.

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

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

Counter target spell. Spells its controller casts cost {2} more to cast this turn.

If you would draw a card, instead exile the top three cards of your library face down. You may look at those cards. Put a card exiled with Brainstorming Session into its owner's hand.
{X}{X}{U}, Sacrifice Brainstorming Session: Put X cards exiled with it into their owner's hand.

When you cast this spell, copy it. You may choose new targets for the copy. (Copies keep functions.)
Draw a card.