msem-instigator

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.

Draw a card. Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Counter target spell with mana value 3 or less. If a spell is countered this way, return it to its owner's hand instead of putting it anywhere else.

Enchant creature
Enchanted creature doesn't untap during its controller's untap step.
At the beginning of the upkeep of enchanted creature's controller, that player mills a card.

Exile target creature. Return that card to its owner's hand at the beginning of its owner's next end step.

Deep-Sea Terror can't attack unless seven or more cards are in your graveyard.

Flash
Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)

{B}{G}, {T}: Reveal the bottom card of your library and exile it. Target creature gets +X/-X until end of turn, where X is that card's mana value.

At the beginning of your upkeep, choose an opponent. That player creates a 3/2 colorless Horror creature token.
{2}: Target opponent gains control of Deepdrinker's Effigy.

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

As an additional cost to cast Deepmire Abomination, reappropriate or pay {2}. (To reappropriate, exile exactly two cards from your hand and/or graveyard.)
Menace

Defender
Sacrifice two Islands: Deepsea Denizen loses defender until end of turn.

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.

Haste
{R}, Sacrifice Deepstone Operative: Destroy target artifact.

Damage dealt by Deepwater Stinger can't be prevented.

Reach (This creature can block creatures with flying.)
Whenever Deepwood Spider blocks a creature with flying, Deepwood Spider gains deathtouch until end of 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.

Augmented — At the beginning of each end step, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, put a +1/+1 counter on Defected Explorer.

Whenever Defective Abomination attacks, you may sacrifice a permanent. If you do, put a +1/+1 counter on it. It gains indestructible until end of turn.

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

Search your library for a basic land card, reveal it, put it into your hand, then shuffle. Create a 1/1 green Elf creature token.