msem-instigator

Flying
Menagerie — When Bleakrealm Mini-Menace enters the battlefield, if there are five or more creature types among creatures you control, it deals 2 damage to target opponent and 2 damage to up to one target creature or planeswalker that player controls.

When Blessing of Roya enters the battlefield or whenever you cast a spell from a graveyard, you gain 5 life and you mill five cards. Then you may put a card from your graveyard on the bottom of your library.

When Blightbringer enters the battlefield, creatures your opponents control get -1/-1 until end of turn.
Unearth {3}{B} ({3}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the end step or if it would leave the battlefield. Unearth only as a sorcery.)

When Blighting Ooze enters the battlefield, put a -1/-1 counter on each of up to X target creatures.
As long as Blighting Ooze is on the battlefield, it has all activated abilities of each creature with a -1/-1 counter on it.

Flash
Blind Blackguard can't block.
When Blind Blackguard enters the battlefield, target player draws a card, then reveals their hand. You choose a nonland card from that player's hand, then that player puts the chosen card on the bottom of their library.

When Blinding Fiddler enters the battlefield, until your next turn, creatures can't attack you or a planeswalker you control unless their controller pays {2} for each of those creatures.
Unveil {3}{W}{U} ({3}{W}{U}: Transform this. Unveil only as a sorcery.)

When Blood Jade Prophet enters the battlefield, reveal the top three cards of your library. For each card revealed this way, you may pay 3 life. If you do, put that card into your hand. Otherwise, put it into your graveyard.

Engorge (As this enters the battlefield, mill three cards, then exile a card from among the milled cards.)
When Blood Servant enters the battlefield, if it engorged a creature card, you draw a card and you lose 2 life.

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Blood-Tithe Harpy enters the battlefield, target player loses 1 life and you gain 1 life.

Enchant creature
When Bloodbriar Blessing enters the battlefield, draw a card.
Enchanted creature gets +2/+2 and has menace.

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

Bloodfell Caves enters the battlefield tapped.
When Bloodfell Caves enters the battlefield, you gain 1 life.
{T}: Add {B} or {R}.

Haste
When Bloodfury Warlord enters the battlefield or dies, it deals 2 damage to each player.

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.

When Bloodpact Tormentor enters the battlefield, you may put a -1/-1 counter on target creature.
Bloodpact Tormentor can't be blocked by creatures with counters on them.

({T}: Add {R}.)
Bloodriver enters the battlefield tapped.
When Bloodriver enters the battlefield, target creature you control gains haste until end of turn.

When Bloodsoaked Blades enters the battlefield, creatures you control get +2/+0 until end of turn.
Equipped creature gets +1/+1.
Equip {1}

Creatures you control that have been dealt damage this turn get +2/+0.
When Bloodspawn enters the battlefield, it deals 1 damage to target creature you control.

Flying, deathtouch
When Bloodsucking Pihuchen enters the battlefield, choose a nonland card name.
Whenever a permanent with the chosen name enters the battlefield, each opponent loses 1 life and you gain 1 life.

When Blossom-Ash Trance enters the battlefield, you gain 3 life.
At the beginning of each end step, if you gained 3 or more life this turn, draw a card.

When Blossom-Sower Witch enters the battlefield, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
Whenever you sacrifice a permanent, you gain 1 life.

Flying
When Blossoming Hatchling enters the battlefield, create a Treasure token.

Blossoming Sands enters the battlefield tapped.
When Blossoming Sands enters the battlefield, you gain 1 life.
{T}: Add {G} or {W}.

Menace
When Bogborn Exorcist enters the battlefield, you may discard a card. When you do, exile target instant or sorcery card with mana value 3 or less from an opponent's graveyard. Copy that card. You may cast the copy without paying its mana cost.

Enchant creature
When Bogfume Pact enters the battlefield, each opponent sacrifices a creature.
When enchanted creature dies, return it to its owner's hand.