Byway Barterer

Menace
Whenever you expend 4, you may discard your hand. If you do, draw two cards. (You expend 4 as you spend your fourth total mana to cast spells during a turn.)

Bakersbane Duo

When Bakersbane Duo enters, create a Food token.
Whenever you expend 4, Bakersbane Duo gets +1/+1 until end of turn. (You expend 4 as you spend your fourth total mana to cast spells during a turn.)

Fetch Quest

Mill seven cards. Then put a creature, enchantment, or land card from among the milled cards onto the battlefield.

Bramble Familiar

{T}: Add {G}.
{1}{G}, {T}, Discard a card: Return Bramble Familiar to its owner's hand.

Bramble Familiar // Fetch Quest

Raccoon Rallier

{T}: Target creature you control gains haste until end of turn. Activate only as a sorcery.

Wandertale Mentor

Whenever you expend 4, put a +1/+1 counter on Wandertale Mentor. (You expend 4 as you spend your fourth total mana to cast spells during a turn.)
{T}: Add {R} or {G}.

Muerra, Trash Tactician

At the beginning of your first main phase, add {R} or {G} for each Raccoon you control.
Whenever you expend 4, you gain 3 life. (You expend 4 as you spend your fourth total mana to cast spells during a turn.)
Whenever you expend 8, exile the top two cards of your library. Until the end of your next turn, you may play those cards.

Birds of Paradise

Junkblade Bruiser

Trample
Whenever you expend 4, Junkblade Bruiser gets +2/+1 until end of turn. (You expend 4 as you spend your fourth total mana to cast spells during a turn.)

Brazen Collector

First strike
Whenever Brazen Collector attacks, add {R}. Until end of turn, you don't lose this mana as steps and phases end.

Scrappy Bruiser

Whenever Scrappy Bruiser attacks, up to one target attacking creature gets +2/+0 and gains trample until end of turn. Return that creature to its owner's hand at end of combat. (Return it only if it's on the battlefield.)

Brambleguard Veteran

Whenever you expend 4, Raccoons you control get +1/+1 and gain vigilance until end of turn. (You expend 4 as you spend your fourth total mana to cast spells during a turn.)

Bark-Knuckle Boxer

Whenever you expend 4, Bark-Knuckle Boxer gains indestructible until end of turn. (You expend 4 as you spend your fourth total mana to cast spells during a turn.)