msem-instigator

Whenever Tide Crasher attacks, if you control another Merfolk, tap target creature defending player controls.

Permanents you control gain indestructible until end of turn. Untap each creature you control.
Cycling {W} ({W}, Discard this card: Draw a card.)

First mate — Each nonland card in your starting deck is an artifact, a Pirate, or has “artifact,” “Treasure,” or “Pirate” in its printed rules text. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Whenever Tinbeard of the Brine attacks, each opponent loses X life and you gain X life, where X is the number of artifacts you control plus the number of Pirates you control.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Crew 1 (Tap any number of creatures you control with total power 1 or greater: This Vehicle becomes an artifact creature until end of turn.)

Flash
When Total Surveillance enters, draw a card.
Whenever you cast another spell with flash or an instant, you may pay {1}. If you do, create a 1/1 colorless Drone artifact creature token with flying.

For each player, you choose from among the permanents that player controls an artifact, a creature, an enchantment, and a planeswalker. Then each player sacrifices all other nonland permanents they control.

Choose a nonland card name. Search target player's graveyard, hand, and library for any number of cards with that name and exile them. That player shuffles. For each card exiled from their hand this way, you discard a card.

For each permanent type, return up to one target card of that type from your graveyard to your hand. (The permanent types are artifact, creature, enchantment, land, and planeswalker.)

Whenever Treasure Hauler attacks, draw a card.
Crew 3 (Tap any number of creatures you control with total power 3 or greater: This Vehicle becomes an artifact creature until end of turn.)

Haste
When Treasure Haulers enters, you may salvage an artifact 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.)

As long as you control three or more artifacts, Treasury Master gets +2/+0 and has slipstream. (This creature can't be blocked as long as only creatures with slipstream are attacking.)

When Trenchbottom Mariners enters, you lose 3 life, mill three cards, and create a Treasure token.
Whenever Trenchbottom Mariners attacks, you may cast a permanent card from your graveyard by sacrificing another artifact in addition to paying its costs.

When Trident of Benediction enters, create two 1/1 white Merfolk creature tokens.
Equipped creature has vigilance and “Whenever this creature attacks or blocks, creatures you control get +1/+1 until end of turn.”
Equip {2}

Pressure {1}{G}{G} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Trample
Whenever Triplicate Monstrosity deals combat damage to a player, draw a card.

Pressure—{2}{U}{U}, Discard your hand. (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
Reveal the top seven cards of your library. Put any number of noncreature, nonland cards from among them into your hand and the rest into your graveyard.

Mountains you control have “{T}: Add {R}{R}.”
[+2]: Exile the top card of your library. You may play that card until the end of your next turn.
[–2]: Conjure six cards named Scorch. Shuffle them and your hand into your library, then draw two cards.

Whenever a creature you control enters, if it wasn't cast, you gain life equal to that creature's toughness and may draw a card.
[+2]: Return up to one target creature card from your graveyard to the battlefield.
[–3]: Create an 8/8 blue Kraken creature token.
[–9]: Each player exiles all creature cards from their graveyard, then sacrifices each creature they control. Put each creature card exiled this way onto the battlefield under your 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.

{1}{R}, Discard a card: Draw a card.
{R}: You may put a creature card from your hand onto the battlefield. That creature gains haste. Activate only if twenty or more cards are in your graveyard.

{1}{U}: Twilight Privateer voyages. (If it isn't blocking or targeted by another spell or ability, it phases out.)
Whenever Twilight Privateer phases in, up to one other target creature voyages.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
{1}{B}, Sacrifice a creature: Put a +1/+1 counter on Twisted Cultist.

Creatures you control dying cause abilities of that creature to trigger as though that creature entered.
{2}{W}{B}, Sacrifice another creature: Destroy target nonland permanent.

You may play Typhoon Caverns from your graveyard as long as seven or more cards are in your graveyard.
Typhoon Caverns enters tapped.
{T}: Add {U} or {B}.
Cycling {1}{U}{B} ({1}{U}{B}, Discard this card: Draw a card.)

{3}{U}: Tap target creature. Activate only as a sorcery.
Cycling {2/U} ({2/U}, Discard this card: Draw a card.)

Haste
Madness {3}{R} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)