msem-instigator

Desecrate (When this creature enters the battlefield, you may sacrifice an artifact or land.)
When Beastback Raider desecrates a permanent, discard your hand, then draw three cards.

Bedfellow can't block or be blocked.
Exile two cards from your graveyard: Bedfellow gets +1/+1 until end of turn.

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

All creatures that aren't embattled get -5/-5 until end of turn. If a creature would die this turn, exile it instead. (A creature is embattled if it has a counter on it or a permanent its owner controls attached to it.)

Enchant creature you control
Enchanted creature gets +3/+3.
When Belligerence enters the battlefield, enchanted creature fights target creature an opponent controls.
When enchanted creature dies, if it's a Warrior, return Belligerence to its owner's 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.

Reprise {4}{G} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)
Target creature gets +3/+3 until end of turn. Then create an X/X green Elk creature token, where X is the amount this spell increased that creature's power.

Flying
Sacrifice six Swamps: Return Berbarus Unsealed from your graveyard to the battlefield with an indestructible counter on it. You draw six cards and you lose 6 life.

{1}{G}: Until your next turn, Bessie becomes a 5/5 green Wurm creature with trample, haste, and indestructible. You can't activate this ability while Bessie is being attacked. (She doesn't lose loyalty while she's not a planeswalker.)
[+1]: Creatures you control get +1/+1 and gain haste until your next turn.
[–6]: Create five 3/3 green Wurm creature tokens with trample and haste.

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

Trample
Bessie's Crusher has haste as long as you control another Wurm.

Return up to two target creature cards with mana value X or less from your graveyard to the battlefield. They can't block this turn.

Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.

Exile target nonland permanent. Its controller gains 5 life.

Return all creature and planeswalker cards from your graveyard to the battlefield.

Pressure {2}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
As an additional cost to cast this spell, sacrifice a creature.
Search your library for a creature card with mana value X or less, where X is equal to twice the sacrificed creature's mana value, put it onto the battlefield, then shuffle.

All creatures get -4/-4 until end of turn.

Whenever a creature card is put into your graveyard from the battlefield, exile it. You lose life equal to that card's mana value. Put it onto the battlefield tapped at the beginning of your next upkeep.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
Return target creature card from your graveyard to the battlefield. If it was put there from the battlefield this turn, create a token that's a copy of it. If you're in a renaissance, create a token that's a copy of it.

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.

Desecrate (When this creature enters the battlefield, you may sacrifice an artifact or land.)
When Bitter Wanderer desecrates a permanent, each opponent loses 2 life and you gain 2 life.

At the beginning of your upkeep, exile the top card of your library. If a land card is exiled this way, add {R}{R}. You don't lose this mana as steps and phases end this turn. Otherwise, you may cast that card this turn.

When Bjarndyr Outfitter enters the battlefield, arm up to two target creatures you control. (Create a colorless Equipment artifact token with “Equipped creature gets +1/+0” and equip {2}, then attach it to that creature.)

Lifelink
Whenever Bjarndyr Sergeant attacks, other creatures you control get +1/+1 and gain lifelink until end of turn.

You lose 1 life and exile the top card of your library. You may repeat this process any number of times. Then put up to two cards exiled this way into your hand.
Coalesce {5}{B}{B} (You may cast this from your graveyard for its coalesce cost. If you do, put it onto the battlefield as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)
Black Hole Musings's power is equal to the number of cards in exile.