Purphoros, God of the Forge

Mana cost: {3}{R}
Type: Legendary Enchantment Creature — God
Power / toughness: 6 / 5
Set: Secret Lair Drop #77 (mythic)

Indestructible
As long as your devotion to red is less than five, Purphoros isn't a creature.
Whenever another creature you control enters, Purphoros deals 2 damage to each opponent.
{2}{R}: Creatures you control get +1/+0 until end of turn.

Purphoros, God of the Forge has 8 printings, first in Theros (2013). EDHREC ranks it #697 among Commander cards. It appears most in Krenko, Mob Boss decks (18,798 on EDHREC). 1 public deck on TCG runs it. It has 12 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 Purphoros, God of the Forge

Break the Chains, led by Caesar, Legion's Emperor

Commanders that run Purphoros, God of the Forge most

Deck counts from EDHREC.

Krenko, Mob Boss: 18,798 decks
Xyris, the Writhing Storm: 8,142 decks
Norin the Wary: 7,971 decks
Baylen, the Haymaker: 6,981 decks
Caesar, Legion's Emperor: 5,665 decks
Zurgo Stormrender: 4,218 decks
Prossh, Skyraider of Kher: 3,558 decks
Esika, God of the Tree // The Prismatic Bridge: 3,414 decks

Often played with Purphoros, God of the Forge

Cards that show up in the same decks on EDHREC.

Rulings

2013-09-15: Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).
2013-09-15: If an activated ability or triggered ability has an effect that depends on your devotion to a color, you count the number of mana symbols of that color among the mana costs of permanents you control as the ability resolves. The permanent with that ability will be counted if it's still on the battlefield at that time.
2013-09-15: Mana symbols in the text boxes of permanents you control don't count toward your devotion to any color.
2013-09-15: Numeric mana symbols ({0}, {1}, and so on) in mana costs of permanents you control don't count toward your devotion to any color.
2020-01-24: Counters put on a God remain on it while it's not a creature, even if they have no effect.
2020-01-24: If a God stops being a creature, it loses the type creature and the creature type God. It continues to be a legendary enchantment.
2020-01-24: The type-changing ability that can make a God not be a creature functions only on the battlefield. It's always a creature card in other zones, regardless of your devotion to its color. It's always a creature spell while it's on the stack.
2020-01-24: When a God enters the battlefield, your devotion to its color (including the mana symbols in the mana cost of the God itself) will determine if a creature entered the battlefield or not for abilities that trigger whenever a creature enters the battlefield.
2020-01-24: The abilities of Gods function as long as they're on the battlefield, regardless of whether they're creatures.
2020-01-24: As a God enters the battlefield, your devotion to its color will determine whether any replacement effects that affect creatures entering the battlefield apply to that God. Because replacement effects are considered before the God is on the battlefield, the mana symbols in its mana cost won't be counted when determining this.
2020-01-24: If an effect causes a God to lose all abilities, its ability that causes it to stop being a creature still applies if appropriate.
2020-01-24: If a God is attacking or blocking and it stops being a creature, it will be removed from combat. It won't rejoin combat if it resumes being a creature later during that combat.