msem-instigator

({T}: Add {U} or {B}.)
Muggy Mire enters tapped unless you control two or more basic lands.

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

({T}: Add {G} or {U}.)
As Mushroom Lagoon enters, you may pay {1}. If you don't, Mushroom Lagoon enters tapped.

When Mystic Mackerel enters, you may have target player mill two cards.
{3}{U}, Sacrifice Mystic Mackerel: Return target enchantment, instant, or sorcery card from your graveyard to your hand.

Haste
Whenever Nadei deals combat damage to a player, that player sacrifices a land. You may put a land card from a graveyard onto the battlefield under your control.

{T}, Discard a card: Draw a card.

Whenever No-Good Gunpointer attacks, you may pay 3 life. If you do, draw a card.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Whenever you cast an enchantment, instant, or sorcery spell, Noble Barracuda gets +1/+0 until end of turn. Scry 1.

Trample
Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
When Nonpareil of the Abyss enters, create an Idol token.
Nonpareil of the Abyss has ward {8} as long as you're in a renaissance.

Flying

Flash
When Notorious Smuggler enters, target opponent reveals their hand. Choose a nonland card revealed this way. Copy it. You may cast the copy this turn. (You still pay its costs, including color. Copies of permanents enter as tokens.)

Flying
Whenever Notorious Windraider attacks, other attacking Pirates and Rogues you control gain flying until end of turn.

Flying, haste
You may reveal each card you draw as you draw it. Whenever you reveal a creature card with mana value 1 or less this way, create a token that's a copy of it. That copy gains haste until end of turn.

Abilities of creatures you activate that aren't mana abilities cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.
{T}: Target creature gains haste until end of turn.

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Tap target creature you don't control.
[Lore III] Tap target creature you don't control. It doesn't untap during its controller's next untap step.

Flash
Ocean's Edge Kraken enters with a hexproof counter on it.
{6}{U}{U}, Remove a hexproof counter from Ocean's Edge Kraken: Return all other creatures to their owners' hands.

Whenever one or more artifacts you control enter, put a +1/+1 counter on Octopus Shiny-Grabber and you gain 1 life.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Concord — Once each turn, when an opponent casts a spell or activates an ability that targets a Merfolk or enchantment you control, you may counter that spell or ability if there are four or more card types among permanents you control.

Other Merfolk you control get +1/+1.
When Olantin Pearlreader enters, scry 2. Then draw a card if you control two or more other Merfolk.

When Old Salt enters, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

Whenever you attack with one or more Pirates, create that many 1/1 white Bird creature tokens with flying that are tapped and attacking. At end of combat, choose one of those tokens, then exile the rest.

Haste (This creature can attack and {T} as soon as it comes under your control.)
Olson's Sky Brigade has flying as long as you control another attacking Pirate.

Flash
Flying

{3}{U}, Exile a card from your graveyard: Omen Serpent can't be blocked this turn.