Core Set 2021

Chandra's Pyreling | Creature | Elemental Lizard | Whenever a source you control deals noncombat damage to an opponent, Chandra's Pyreling gets +1/+0 and gains double strike until end of turn. (It deals both first-strike and regular combat damage.) | Josu Hernaiz

Heartfire Immolator | Creature | Human Wizard | Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.) {R}, Sacrifice Heartfire Immolator: It deals damage equal to its power to target creature or planeswalker. | Donato Giancola

Unleash Fury | Instant | | Double the power of target creature until end of turn. | Izzy

Volcanic Geyser | Instant | | Volcanic Geyser deals X damage to any target. | Clint Cearley

Alpine Houndmaster | Creature | Human Warrior | When Alpine Houndmaster enters the battlefield, you may search your library for a card named Alpine Watchdog and/or a card named Igneous Cur, reveal them, put them into your hand, then shuffle. Whenever Alpine Houndmaster attacks, it gets +X/+0 until end of turn, where X is the number of other attacking creatures. | Mark Behm