msem-instigator

{T}: Target land you control becomes the basic land type of your choice until end of turn.
At the beginning of each end step, if you spent three or more colors of mana to cast spells this turn, surveil 1.

({T}: Add {W} or {U}.)
As Lakeside Park enters, you may pay {1}. If you don't, Lakeside Park enters tapped.

Whenever you cast a spell during another player's turn, monstrosity 1. (If this creature isn't monstrous, put a +1/+1 counter on it and it becomes monstrous.)

Kindle 4—{4}{U}{U} ({4}{U}{U}, Exile this card from your graveyard: Create four 1/1 colorless Elemental creature tokens. Kindle only as a sorcery.)

Haste
You may cast sorcery and enchantment spells as though they had flash.
Whenever you cast an enchantment, instant, or sorcery spell, Lightning-Fast Lionfish gets +1/+0 and gains first strike until end of turn.

When Lilyreed Triton enters, create a white Aura enchantment token named Triton's Gift attached to target creature. The token has enchant creature and “Enchanted creature gets +1/+0 and can't be blocked by creatures with power 3 or greater.”

When Lionfrill Hunter enters or when you cycle it, put X +1/+1 counters on another target creature you control, where X is the number of cards with a cycling ability in your graveyard.
Cycling {3}{R}{G} ({3}{R}{G}, Discard this card: Draw a card.)

Whenever you gain life, put a +1/+1 counter on Listless Maneli.
Surpass {5}{W} ({5}{W}: Transform this creature. This costs {1} less to activate for each counter on it. Activate only as a sorcery.)

Trample
Whenever Living Archipelago enters or attacks, up to two target lands you control voyage. (If they aren't being targeted by another spell or ability, they phase out.)
Whenever a land you control phases in, you may create a tapped token that's a copy of that land.

Flying
Long-Finned Skywhale can block only creatures with flying.

Other Merfolk you control get +1/+1.
{1}{U}: Target Merfolk gains slipstream until end of turn. (Creatures with slipstream can't be blocked as long as only creatures with slipstream are attacking.)

Lumbering Stoneshell has hexproof as long as it's untapped.

When Lurking Angler enters, if seven or more cards are in your graveyard, draw a card. Otherwise, mill two cards.

({T}: Add {G} or {U}.)
Lush Oasis enters tapped unless you control a basic Forest or a basic Island.

Other Pirates and Rogues you control get +1/+0.
Whenever you attack with three or more Pirates and/or Rogues, tap target creature.

Attacking Pirates and Rogues you control get +1/+0.
{2}{U}: Tap target creature an opponent controls.

First mate—Each nonland card in your starting deck is an instant or has flash. (If this card outside the game is your chosen first mate, you may swap it with a card in your opening hand.)
Flash
When Mable enters, you gain 2 life and draw a card.

Flash (You may cast this spell any time you could cast an instant.)
When Majestic Hippocamp enters, target creature gets -2/-0 until end of turn.

Flying
Whenever a permanent you control is returned to your hand, scry 1.

Majestic Nauticorn has first strike as long as it's attacking.
Cycling {W} ({W}, Discard this card: Draw a card.)

Dominance — When Mammoth Crab enters, draw a card if you control the creature with the greatest power or tied for the greatest power.

Pressure {G} (You may cast this spell for its pressure cost if there are seven or more cards in your graveyard.)
Deathtouch

Whenever you cast a spell from anywhere other than your hand, surveil 1.

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.”

Whenever Marine Delver attacks, draw a card.