Combine Guildmage

{1}{G}, {T}: This turn, each creature you control enters with an additional +1/+1 counter on it.
{1}{U}, {T}: Move a +1/+1 counter from target creature you control onto another target creature you control.

Brineborn Cutthroat

Flash (You may cast this spell any time you could cast an instant.)
Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on this creature.

Coral Fighters

Whenever this creature attacks and isn't blocked, look at the top card of defending player's library. You may put that card on the bottom of that player's library.

Benthic Biomancer

{1}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on this creature, draw a card, then discard a card.

Bioluminary

Whenever Bioluminary deals combat damage to a player, you get {TK}{TK}, then you may put a sticker on a nonland permanent you own.

Cosi's Trickster

Whenever an opponent shuffles their library, you may put a +1/+1 counter on this creature.

Caller of Gales

{1}{U}, {T}: Target creature gains flying until end of turn.

Deeproot Champion

Whenever you cast a noncreature spell, put a +1/+1 counter on this creature.

Augur of Bolas

When this creature enters, look at the top three cards of your library. You may reveal an instant or sorcery card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Deeproot Elite

Whenever another Merfolk you control enters, put a +1/+1 counter on target Merfolk you control.