Torrential Gearhulk

Mana cost: {4}{U}{U}
Type: Artifact Creature — Construct
Power / toughness: 5 / 6
Set: Commander Masters #501 (rare)

Flash
When this creature enters, you may cast target instant card from your graveyard without paying its mana cost. If that spell would be put into your graveyard, exile it instead.

Torrential Gearhulk has 7 printings, first in Kaladesh (2016). EDHREC ranks it #2,688 among Commander cards. It appears most in Fire Lord Azula decks (10,886 on EDHREC). 1 public deck on TCG runs it. It has 3 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 Torrential Gearhulk

Scions & Spellcraft - Final Fantasy Commander, led by Y'shtola, Night's Blessed

Commanders that run Torrential Gearhulk most

Deck counts from EDHREC.

Often played with Torrential Gearhulk

Cards that show up in the same decks on EDHREC.

Rulings

2016-09-20: If you cast the card, you do so as part of the resolution of Torrential Gearhulk's triggered ability. You can't wait to cast it later in the turn. Timing restrictions (such as "Cast [this card] only during combat") still apply.
2016-09-20: If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs, such as emerge costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Incendiary Sabotage, you must pay those to cast the card.
2016-09-20: If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.