msem-instigator

Flying, first strike, haste
Whenever Doombringer Dragon attacks, you may sacrifice another creature. If you do, Doombringer Dragon gets +3/+0 until end of turn.

Deathtouch
When Doomed Explorer dies, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Vanishing 4 (This permanent enters with four time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
When Doomed Fate leaves the battlefield, if it had no time counters on it, destroy all nonland permanents.

Enchant creature
Enchanted creature gets -2/-2.
At the beginning of the upkeep of enchanted creature's controller, that player discards a card.

Menace
When Doomed Questant enters, each opponent sacrifices a creature and discards a card.

When Doomed Traveler dies, create a 1/1 white Spirit creature token with flying.

When Doomed Widow dies, create a 1/1 white Spirit creature token with flying.

When Doomed Woodsman dies, create a 1/1 green Faerie Druid creature token with hexproof.

Doomsday Horde enters tapped unless it was foreshadowed.
When Doomsday Horde dies, search your library for a card, put it into your hand, then shuffle.
Foreshadow {3}{B}{B}{B} (You may cast this spell for its foreshadow cost. If you do, also trigger its “dies” abilities when it enters.)

Whenever Doomsower or another Human you control dies, you draw a card and you lose life equal to that creature's power.

When Doomstep Giant enters, each player sacrifices a land.

Whenever you cast your second spell each turn, you may have Dormant Memory phase out until you cast your second spell in a turn. (While phased out, treat it and anything attached to it as though they don't exist.)
Fleeting {1}{U} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

Enchant creature
When Double Arming enters, put a +1/+1 counter on enchanted creature.
Enchanted creature has menace.
{5}: Return Double Arming to its owner's hand.

First strike, haste
Whenever you cast a spell, Double-Edged Duelist gains double strike until end of turn if that spell has the same name as a card in your graveyard.

Return target nonland permanent you control and target nonland permanent you don't control to their owners' hands.
{2}{U}, Exile Doubt Oneself from your graveyard: Search your library for a card named Study Oneself, reveal it, put it into your hand, then shuffle.

Other creatures you control get +1/+1.
Lands you control enter tapped.

Double strike, trample
Enchantment spells you cast cost {1} less to cast.
Whenever you put a lore counter on a Saga you control, Douglass, Star of the Show gets +1/+1 until end of turn.

Douse in Flame deals 5 damage to target creature without flying. When that creature leaves the battlefield this turn, exile its controller's graveyard.

{T}, Sacrifice an Equipment: Return target Equipment card from your graveyard to the battlefield. Activate only as a sorcery.

Primal—Reappropriate green. (During your turn, you may cast this spell by exiling two green cards from your hand and/or graveyard instead of playing a land.)
When Dovon's Masterwork enters, return target land card from your graveyard to the battlefield tapped.

{T}: Add {G}.
{B/G}, {T}: Exile target card from a graveyard. If that card is a creature card, put a +1/+1 counter on Dovon, Verdant Experimenter and you gain 1 life.

Whenever another creature dies, you gain 1 life.
At the beginning of each end step, if you gained 3 or more life this turn, transform Dowager of Traublassen.

This spell costs {2} less to cast if you control a Rogue.
Target opponent discards two cards.

Enchant opponent
When Down with the Ship enters, enchanted player discards a card unless they sacrifice a creature.
{1}{B}, Sacrifice Down with the Ship: Return target creature card from your graveyard to your hand.

First mate — Twelve or more cards in your starting deck have “gain control” or “exchange control” in their printed rules text. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Dr. Telsi of the Ark can't be blocked.
Dr. Telsi gets +1/+1 for each permanent you control but don't own.