msem-instigator

Barbed Reef enters tapped. When it does, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this, then you may put that card into your graveyard.)
{T}: Add {B}.
{4}{B}: Barbed Reef becomes a Jellyfish creature. (This effect lasts indefinitely.)

When Barking Irons enters, if it's not a token, create a token that's a copy of it.
Equipped creature gets +2/+0.
Equip {2}

Equipped creature gets +2/+2.
Equip {3}

Equipped creature gets +1/+1 for each permanent attached to it and has trample.
Equip {4}

Barren Boneyard enters tapped.
{T}: Add {B}.
{2/B}{2/B}: Barren Boneyard becomes a 2/3 black Elemental creature with deathtouch until end of turn. It's still a land.

As Barren Desolation enters, you may pay 2 life. If you don't, Barren Desolation enters tapped.
{T}, Sacrifice Barren Desolation: Search your library for a Plains or Swamp card, put it onto the battlefield, then shuffle.

Barren Vista enters tapped.
{T}: Add {U} or {B}.
{1}, {T}: Add one mana of any color.

Each planeswalker you control enters with an additional loyalty counter on it.
{T}: Add {C}.

Whenever you untap a nonland permanent, put a winding counter on Barton's Pocketwatch.
{T}: Look at the top card of your library. You may put it into your graveyard. Then if Barton's Pocketwatch has twelve or more winding counters on it, exile it and take an extra turn after this one.

Basin Fortress enters tapped unless you control a basic land.
{T}: Add {B} or {G}.

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast enchantment spells or to activate an ability of an enchantment.
When Bastion, Node of the Free is destroyed, return it to its owner's hand.

Equipped creature gets +1/+1.
As long as equipped creature is a Soldier or Warrior, it gets an additional +1/+1.
Equip {1}

{4}{G}: Battle Station gets +3/+3 until end of turn.
Cycling {2/G} ({2/G}, Discard this card: Draw a card.)

At the beginning of your upkeep, Bauble of Infinites deals 2 damage to each opponent and you gain 2 life.

(Transform this if it's not attached to a creature. Pay {1}{U} as a sorcery to unattach it.)
Enchant creature you control
Bay-Bandit's Snapper's rider gets +1/+2.
Whenever Bay-Bandit's Snapper's rider deals combat damage to a player, you draw two cards.

When Bearer of Old Growth enters, choose one —
• Untap up to two target artifacts.
• Draw a card.

Equipped creature has menace and trample.
Equip {2}

Whenever you cast an instant or sorcery spell, each opponent loses 1 life and Beast of Pestilence gets +1/+1 until end of turn.

{T}: Add one mana of any color.
{2}, {T}: Put a lore counter on a Saga you control.

(Transform this if it's not attached to a creature. Pay {2}{B}{B} as a sorcery to unattach it.)
Enchant creature you control
Belmord Blood-Coach's rider gets +3/+3 and has deathtouch.
Whenever Belmord Blood-Coach's rider attacks, you may return target creature card with mana value less than its rider's power from your graveyard to the battlefield tapped.

Whenever equipped creature attacks, it gets +X/+0 until end of turn, where X is its power.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Enchant creature
At the beginning of the upkeep of enchanted creature's controller, Betrayer's Mantle deals 3 damage to that player.

Bigroot Valley enters tapped.
{T}: Add {R} or {G}.
{1}, {T}: Add one mana of any color.