msem-instigator

When Deathless Hunter dies, you may put it on the bottom of its owner's library.

You don't lose the game for having 0 or less life.
Whenever you're dealt damage, mill that many cards.
{B}, Pay 2 life: Put target card in your graveyard on the bottom of your library.

You may exert Deathmarked Explorer as it attacks. When you do, it gets +X/+X until end of turn, where X is 10 minus your life total. (An exerted creature won't untap during your next untap step.)
{T}, Discard a card: Draw a card. Deathmarked Explorer deals 2 damage to you.

Creatures you control have menace.

{T}: Add {C}.
{T}, Exile two cards from your graveyard: Add {W} or {B}.

Deathwind Survivor's power and toughness are each equal to the number of enchantments you control.
Whenever an enchantment you control enters, put a +1/+1 counter on target creature.

When Debaser of Truth enters, if you control three or more Horrors, each opponent discards two cards.
Other Horror creatures you control get +1/+1.

{T}: Put a flood counter on Decanter of Endless Rivers. Add {U} for each flood counter on it.

Decay deals damage to creatures in the form of -1/-1 counters.
{B}{G}: Until end of turn, target creature deals damage to creatures in the form of -1/-1 counters. Activate only if Decay is in your graveyard.

Deception can't be blocked.
{1}{U}{B}: Target creature can't be blocked this turn. Activate only if Deception is in your graveyard.

Flash
When Decisive Arcanist enters, you may cast target modal instant or sorcery card in your graveyard. Exile that card instead of putting it into your graveyard as it resolves.

Whenever another creature you control enters, you may change Declan, Wayward Squire's base power and toughness to that creature's power and toughness until end of turn.

Indestructible (Damage and effects that say “destroy” don't destroy this creature.)
Whenever Declare, the Mother Bear deals combat damage to a player, put a +1/+1 counter on it.

Counter target creature spell, planeswalker spell, or activated ability.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever a player activates an ability of an artifact, creature, or land, if it isn't a mana ability, Dedicated Weaponsmith deals 2 damage to that player.

Deepdrinker's Domain enters tapped.
{T}: Add {U}.

Deeplife Cavern enters tapped unless you control a Forest.
{T}: Add {U} or {B}.

Menace
Creatures you control get +1/+0 as long as you've foretold a card this turn.
Creatures you control get +1/+0 as long as you've cast a foretold spell this turn.

Destroy target creature or planeswalker.
Compose (Then if you cast this from your hand, exile it and create a Saga token with “r3—You may cast a copy of this card from exile without paying its mana cost.”)

As long as it's your turn, Defect 37 is a 7/7 Vehicle artifact with crew 2.
[+1]: Creatures and Vehicles you control get +1/+1 until end of turn.
[–1]: Put target permanent into its owner's library, third from the top. If Defect 37 is on the battlefield, return her to her owner's hand.
[–6]: Until end of turn, each noncreature, nonland permanent you control becomes a creature in addition to its other types with base power and toughness each equal to their mana value or base power, whichever is greater.

{T}: Add {C}.
{3}{R}: Until end of turn, Defect's Precinct becomes a 3/3 creature. It's still a land. It has trample if {G} was spent to activate this ability, has vigilance if {W} was spent, and has hexproof if {U} was spent.

Archive 5 (As this enters, shuffle the top five cards of your main library into a new face up library. Sacrifice this after the archived library is empty.)
Whenever you draw a permanent card from the archived library, you may have Defect's Study become a copy of it until end of turn.

Whenever you cast a spell, if it shared a color with the last spell you cast this turn, put two +1/+1 counters on Defected Android.

Spells can't be cast from libraries.
If a nonland permanent would enter from a library, exile it instead.

Flying, vigilance
Whenever you attack, if you've cast a spell from a graveyard this turn, you may pay {1}{W}. If you do, put Defender of Carü Mapu from your graveyard onto the battlefield. It's attacking.