msem-instigator

Whenever Apostle of the Spirit Moon becomes blocked by a creature, Apostle of the Spirit Moon deals 1 damage to that creature and that creature's controller.

Ashthread Alley enters tapped.
{T}: Add {B} or {R}.
{B}{R}, {T}, Sacrifice Ashthread Alley: Conjure a card named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

Flying
When Azos enters, each opponent reveals their hand. You choose any number of nonland cards in players' hands and/or creatures on the battlefield with total mana value 7 or less. Exile those cards and/or permanents.

First strike
Back-Alley Gnoll has lifelink as long as it's enchanted by a black Aura.
Back-Alley Gnoll gets +2/+0 as long as it's enchanted by a red Aura.

Menace
As long as Balefire Harbinger is attacking, creatures in its pack can't be blocked unless defending player pays {1} and 1 life for each creature they control that's blocking one of those creatures. (Two or more creatures you control with equal power are in a pack.)

Whenever Barker Duelist becomes blocked, defending player loses 1 life.
Unveil {3}{B}{R} ({3}{B}{R}: Transform this. Unveil only as a sorcery.)

When Basalt Ritualist enters, you may sacrifice a land or exile a land card from your graveyard. When you do, exile target creature, instant, or sorcery card from your graveyard. Until the end of your next turn, you may play that card. If that spell would be put into a graveyard, exile it instead.

Haste
Glorious end — When Battle-Blind Leonin dies, if it was tapped, you may pay {B}. If you do, you draw a card and you lose 1 life.

Menace
When Beatrice enters, target opponent reveals their hand. Exile a nonland card from it. During any turn that player lost life, you may cast that card and mana of any type can be spent to cast that spell.

Whenever Beatrice's Dodger attacks, create a 1/1 black and red Human Rogue creature token that's tapped and attacking.
{3}{B}{R}: Return Beatrice's Dodger from your graveyard to the battlefield
tapped and transformed.

Flying
When Blackblood Feaster enters, you may have each player sacrifice a creature.
Pay 2 life: Blackblood Feaster gets +2/+2 until end of turn. Activate only once each turn.

Bleakrealm Moor enters tapped unless you played it from exile.
{T}: Add {B} or {R}.

Flying
Glorious end — When Blinded Avenger dies, if it was tapped, destroy target creature you don't control.

Target creature gets +3/-3 until end of turn.
Kindle 3—{B}{R}, Pay 3 life. ({B}{R}, Pay 3 life, Exile this card from your graveyard: Create three 1/1 colorless Elemental creature tokens. Kindle only as a sorcery.)

Nonbasic lands have “Whenever this land becomes tapped, you lose 1 life unless you sacrifice this land.”

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
Each opponent discards a card and loses 2 life.
Exile target card from a graveyard. If a creature card was exiled this way, you gain 2 life.
At the beginning of the next end step, you gain 3 life if an opponent lost life this turn and each opponent loses 3 life if you've gained life this turn.

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

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

Bloodsand Gulch enters tapped unless you control another Desert.
{T}: Add {B} or {R}.

Other Warriors you control get +2/+0.
Whenever a Warrior you control dies, Bloodshed Devotee deals 1 damage to target opponent.

Bloodstone Halls enters tapped unless you control two or more black and/or red permanents.
{T}: Add {B} or {R}.

Whenever a creature with a counter on it dies, create a Gold token. (It's an artifact with “Sacrifice this artifact: Add one mana of any color.”)

{T}: Add {C}.
{1}, {T}: Add {B}{R}.

First strike
Ascend {1}{B} ({1}{B}: Exile this creature, then return it to the battlefield transformed. Ascend only as a sorcery.)

Flying
When Calamity Harbinger enters, it deals 4 damage to up to one target creature or planeswalker.