Scaretiller

Whenever Scaretiller becomes tapped, choose one —
• You may put a land card from your hand onto the battlefield tapped.
• Return target land card from your graveyard to the battlefield tapped.

Gideon's Avenger

Whenever a creature an opponent controls becomes tapped, put a +1/+1 counter on Gideon's Avenger.

Hangar Scrounger

Backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following ability until end of turn.)
Whenever this creature becomes tapped, you may discard a card. If you do, draw a card.

Samite Herbalist

Whenever Samite Herbalist becomes tapped, you gain 1 life and scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Spireside Infiltrator

Whenever Spireside Infiltrator becomes tapped, it deals 1 damage to each opponent.

Goblin Medics

Whenever Goblin Medics becomes tapped, it deals 1 damage to any target.

Rhoda, Geist Avenger

Partner with Timin, Youthful Geist (When this creature enters, target player may put Timin into their hand from their library, then shuffle.)
Vigilance
Whenever a creature an opponent controls becomes tapped, if it isn't being declared as an attacker, put a +1/+1 counter on Rhoda, Geist Avenger.

Stun Sniper

{1}, {T}: Stun Sniper deals 1 damage to target creature. Tap that creature.

Stonybrook Schoolmaster

Whenever Stonybrook Schoolmaster becomes tapped, you may create a 1/1 blue Merfolk Wizard creature token.

Renegade Wheelsmith

Whenever Renegade Wheelsmith becomes tapped, target creature can't block this turn.

Reckless Racer

First strike
Whenever Reckless Racer becomes tapped, you may discard a card. If you do, draw a card.

Attentive Sunscribe

Whenever Attentive Sunscribe becomes tapped, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Judge of Currents

Whenever a Merfolk you control becomes tapped, you may gain 1 life.

Volatile Wanderglyph

Whenever Volatile Wanderglyph becomes tapped, you may discard a card. If you do, draw a card.