msem-instigator

At the beginning of your upkeep, if six or more cards are in your graveyard, you may transform Scuttling Gnat.

{1}{B}, Sacrifice a creature: You gain 1 life and draw a card.
{4}{B}, Pay 3 life, Sacrifice Traverse the Endless Well: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.

({T}: Add {U} or {B}.)
Whenever Murmuring Falls becomes tapped, you lose 1 life unless you control two or more basic lands.

Whenever you cast a noncreature spell, Runeclad Seeker gets +1/+1 until end of turn. If that spell was an Aura or Equipment spell, put a +1/+1 counter on Runeclad Seeker instead.

Menace (This creature can't be blocked except by two or more creatures.)

Whenever Skeigr, Skhorvall Flagship attacks, it deals 3 damage divided as you choose among one, two, or three targets.
Crew 3 (Tap any number of creatures you control with total power 3 or greater: This Ship Vehicle becomes an artifact creature until end of turn.)

Flash
Heretic (Whenever you cast a spell that doesn't share a color with this creature, it gets +1/+1 until end of turn.)

First strike
Sacrifice Fearless General: Soldiers you control gain indestructible until end of turn.

Enchant creature
Enchanted creature gets -4/-0.
Mirage {U} (You may cast this spell as though it had flash for its mirage cost. If you do, sacrifice it at the beginning of the next cleanup step.)

This spell costs {2} less to cast if you control an embattled creature. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)
Destroy target tapped creature.

When Gift of the Seraph enters, exile target nonland permanent an opponent controls until Gift of the Seraph leaves the battlefield. When you do, create a Weapon token and attach it to up to one target creature you control. (A Weapon token is an Equipment artifact with “Equipped creature gets +1/+1” and equip {2}.)

Untap all creatures you control.
Draw a card.

Creatures you control have “Whenever this creature attacks, put a +1/+1 counter on target creature with lesser power.”
At the beginning of each end step, if there are five or more +1/+1 counters among creatures you control, destroy up to one target artifact or enchantment.

Disgraced 5 (This enters with five -1/-1 counters. Whenever it deals combat damage to a player, remove all -1/-1 counters from it.)
Prevent all combat damage that would be dealt to Heir Unapparent.

Scry 5.

Reach, deathtouch

Enchant creature
Enchanted creature has infiltrate. (Whenever one or more attacking creatures you control aren't blocked, enchanted creature gets +1/+1 until end of turn.)
Whenever enchanted creature deals combat damage to a player, draw a card.

Whenever a Monkey creature you control becomes the target of a spell or ability, you may reveal the top card of your library. If you do, counter that spell or ability if it has the same mana value as the revealed card. (Abilities have a mana value of 0.)

When Felhide Marauder enters, if you control a creature with power greater than its base power, Felhide Marauder gains haste until end of turn.

When Envoy of Growth enters, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Flying
When Old-World Forgotten dies, you may return target artifact or enchantment card from your graveyard to your hand.

Flying
Whenever Archon of Inspiration attacks, add three mana in any combination of colors at the beginning of your next main phase.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Whenever Manipulator of Waves attacks, mill three cards. Then create a 0/0 blue Elemental Serpent creature token with “This creature gets +1/+1 for each five cards in your graveyard.”

Trample
Ride {3}{G} ({3}{G}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)

When Compulsion's Voice enters, gain control of target permanent until end of turn. Untap that permanent. It gains haste until end of turn.
Recite {1}{U}{R} (You may cast this creature from your graveyard for its recite cost. If you do, exile it when it enters or if it would leave the battlefield.)