msem-instigator

Whenever you cast a spell, if it isn't your main phase, you may have Stoneshrine Guardian's base power and toughness become 4/1 or 1/4 until end of turn.

Whenever one or more creatures you control deal combat damage to a player, exile a nonland card from that player's graveyard. Copy it. You may cast the copy. (You still pay its costs, including color. Copies of permanents enter as tokens.)

At the beginning of your upkeep, you may pay 2 life. If you do, exile the top card of target opponent's library. If a nonland card is exiled this way, copy it. You may cast the copy. (You still pay its costs, including color. Copies of permanents enter as tokens.)

Flash
Flying
When Strange Sights dies, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

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.

When Stygian Leviathan enters, target opponent loses life equal to the number of Curses attached to them and you gain that much life.

First strike, vigilance
When Subnautical Legionnaire enters, choose artifact, enchantment, or Merfolk. Exile target nonland permanent you don't control until you control no permanents of the chosen type.

At the beginning of your upkeep, Suitor of the Sea deals 1 damage to each player.

{W}: Target creature gains vigilance until end of turn.

Flying
When Sunchaser Mantas enters, choose a color. Look at the top four cards of your library. You may reveal a card of the chosen color from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Heretic (Whenever you cast a spell that doesn't share a color with this creature, it gets +1/+1 until end of turn.)
{1}{W}: You gain life equal to Sunken Outcast's power.

Primal {1}{W}{W} (During your turn, you may cast this spell for {1}{W}{W} instead of playing a land.)
Double strike
When Sunken Slasher enters, if you didn't play a land this turn, put a +1/+1 counter on it.

Pressure {3}{B}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
When Sunken-Eye Angler enters, mill three cards. Then if it was cast for its pressure cost, you may return a creature card from your graveyard to the battlefield.

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

Haste
{T}, Discard a card: Flip a coin. If you win the flip, draw two cards. Otherwise, you may pay {R}. If you do, repeat this process.

Haste
At the beginning of combat on your turn, target creature or Vehicle you control gets +2/+0 until end of turn.

When Syzygy Navigator enters, exile target nonland card from an opponent's graveyard. Copy it. You may cast the copy. (You still pay its costs, including color. Copies of permanents enter as tokens.)
Whenever you cast a spell from anywhere other than your hand, draw a card, then discard a card.

During each of your turns, you may cast a copy of a card in an opponent's graveyard by exiling that card in addition to its other costs. (Copies of permanents enter as tokens.)

First mate—Your starting deck contains no more than eight cards of each nonland card type. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Lifelink
At the beginning of your upkeep, you may pay 3 life. If you do, exile another target nonland permanent until Tabia leaves the battlefield. If you control another permanent that shares a card type with it, exile it instead.

Indestructible
If Tarraka-no-Oni would be put into a graveyard from anywhere, reveal Tarraka-no-Oni and shuffle it into its owner's library instead.

Flying
When Tempest Stormcaster enters, if a permanent you control left the battlefield this turn, you may have target player draw a card.

When you unveil Tempest Termagant, you may put target land on top of its owner's library.

Flying
{T}: Target land you control becomes the basic land type of your choice until end of turn.

Protection from nonblue
Whenever Terror of Palta Gorge attacks, exile another target nonblue creature until Terror of Palta Gorge leaves the battlefield.

Heroic — Whenever you cast a spell that targets Thassa's Shoreguards, tap target creature an opponent controls. It doesn't untap during its controller's next untap step.
Whenever Thassa's Shoreguards deals combat damage to a player, draw a card.