msem-instigator

Flash
Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
When Grim enters, if you sacrificed a permanent this turn, exile target tapped creature.

Whenever two or more creatures you control deal combat damage to a player, you gain 3 life and create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)
Whenever you sacrifice your second permanent each turn, you draw a card and you lose 1 life.

Whenever you cast an artifact or enchantment spell, scry 1, then create a 1/1 white Merfolk creature token.
Whenever you cast a Merfolk spell, look at the top card of your library. If it's an artifact or enchantment card, you may reveal it and put it into your hand.

When Duchess Odelia VII enters, search your library for a nonland permanent card with mana value 1 or less, reveal it, put it into your hand, then shuffle.

Pressure {3}{U}{B} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Destroy up to one target creature. Return all other nonland permanents to their owners' hands.

Menace
Other artifact creatures you control have menace.
{2}{B}{R}: Salvage an artifact or creature card. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

When Dawson's Warden enters, create a Treasure token.
As long as you control three or more artifacts, Dawson's Warden gets +2/+0 and has first strike.

Pressure {3}{U}{B} (You may cast this spell for its pressure cost if there are seven or more cards in your graveyard.)
Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
{U}{B}, Reveal Cuxuri Beckoner from your hand: Target player mills two cards.

When Coralight Paladin enters, you may search your library for an artifact card, reveal it, then shuffle and put that card on top.
Concord — Whenever Coralight Paladin attacks, if there are four or more card types among permanents you control, Merfolk you control get +1/+1 until end of turn.

Pressure {B}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Search your library and/or graveyard for a creature card with mana value 3 or less and put it onto the battlefield. If you searched your library this way, shuffle.

At the beginning of each end step, if you drew and/or discarded six or more cards this turn, return Anemothrys, Reefcrown from your graveyard to the battlefield.
Cycling {R}{G} ({R}{G}, Discard this card: Draw a card.)

Whenever you draw your second card each turn, put a +1/+1 counter on Youthful Tortoise.
Cycling {2} ({2}, Discard this card: Draw a card.)

Destroy target artifact or enchantment.
Cycling {2} ({2}, Discard this card: Draw a card.)

Pressure {3}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Put two +1/+1 counters on target creature you control if Way of the Danithra was cast for its pressure cost. Then it fights up to one target creature you don't control.

Pressure {5}{G}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Search your library for three creature cards and reveal them. Put one onto the battlefield, one into your hand, the rest into your graveyard, then shuffle.

Concord — At the beginning of combat on your turn, if there are four or more card types among permanents you control, Sturdyshell Hammerclaw gets +2/+1 and gains trample until end of turn.

Target creature gets +3/+3 until end of turn.
Cycling {2} ({2}, Discard this card: Draw a card.)

Whenever Silt Lurker deals combat damage to a player, mill three cards, then draw a card if seven or more cards are in your graveyard.
Cycling {G} ({G}, Discard this card: Draw a card.)

Pressure {2}{G}{G} (You may cast this spell for its pressure cost if there are seven or more cards in your graveyard.)
Trample, hexproof
Shambling Dreadreef's power and toughness are each equal to the total number of land cards you own on the battlefield and in your graveyard.

Seafoam Slasher gets +1/+1 and has deathtouch as long seven or more cards are in your graveyard.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Seafloor Wreckage enters and when you sacrifice it, search your library for a basic land card, reveal it, put it into your hand, then shuffle.
{1}{G}, Sacrifice Seafloor Wreckage: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

Concord — {1}{G}: Until end of turn, Seadrake Rider gets +2/+3 and must be blocked if able. Activate only during your turn, only once each turn, and only if there are four or more card types among permanents you control.

Pressure {1}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Search your library for three basic land cards and reveal them. Put one onto the battlefield tapped, one into your hand, the rest into your graveyard, then shuffle.

[+1]: Create a tapped colorless artifact token named Conch Shell with “{T}: Add one mana of any color. Spend this mana only to cast permanent spells.”
[–1]: Reveal the top X cards of your library, where X is the number of card types among permanents you control. Put a permanent card from among them into your hand and the rest into your graveyard.
[–3]: Create two 3/3 red Shark enchantment creature tokens.