Tectonic Giant

Mana cost: {2}{R}{R}
Type: Creature — Elemental Giant
Power / toughness: 3 / 4
Set: Theros Beyond Death Promos #158p (rare)
Price: $0.32 USD

Whenever this creature attacks or becomes the target of a spell an opponent controls, choose one —
• This creature deals 3 damage to each opponent.
• Exile the top two cards of your library. Choose one of them. Until the end of your next turn, you may play that card.

Tectonic Giant has 9 printings, first in Theros Beyond Death (2020). EDHREC ranks it #3,152 among Commander cards. It appears most in Isshin, Two Heavens as One decks (7,593 on EDHREC). 4 public decks on TCG run it. It has 7 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Public decks that run Tectonic Giant

Chaos Incarnate - Starter Commander Decks, led by Kardur, Doomscourge
Endless Punishment - Duskmourn: House of Horror Commander, led by Valgavoth, Harrower of Souls
Exit from Exile - Commander Legends: Battle for Baldur's Gate, led by Faldorn, Dread Wolf Herald
Planar Portal - Forgotten Realms Commander, led by Prosper, Tome-Bound

Commanders that run Tectonic Giant most

Deck counts from EDHREC.

Isshin, Two Heavens as One: 7,593 decks
Valgavoth, Harrower of Souls: 5,000 decks
Indoraptor, the Perfect Hybrid: 2,421 decks
Prosper, Tome-Bound: 2,228 decks
Faldorn, Dread Wolf Herald: 2,046 decks
Aegar, the Freezing Flame: 1,999 decks
Torbran, Thane of Red Fell: 1,660 decks
Neheb, the Eternal: 1,615 decks

Often played with Tectonic Giant

Cards that show up in the same decks on EDHREC.

Rulings

2020-01-24: Tectonic Giant doesn't change when you can play the exiled card. For example, if you exile a sorcery card, you can cast it only during your main phase when the stack is empty. If you exile a land card, you can play it only during your main phase and only if you have an available land play remaining.
2020-01-24: Playing an exiled card causes it to leave exile. You can't play it multiple times.
2020-01-24: An ability that triggers when a creature becomes the target of a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
2020-01-24: If you don't play the exiled card that you chose, it remains in exile with the card you didn't choose.
2020-01-24: Players can cast spells and activate abilities after the triggered ability resolves but before the spell that caused it to trigger does.
2020-01-24: If a spell targets Tectonic Giant more than once, its ability triggers only once.
2020-01-24: You choose which of the exiled cards you'll be able to play while the ability is resolving. You can't wait to pick one later. The other card remains in exile.