What it does
Fire Fang is a Fire-type physical move in the bite/fang category, with two separate secondary effects: a chance to burn the target, and a chance to cause flinching. Both can trigger independently on the same hit — neither is guaranteed, but they're separate rolls, so you can get both, one, or neither on any given use.
Burn chips the target each end of turn and cuts their physical Attack in half — a real downside for physical attackers. Flinch prevents the target from acting that turn, but only matters if you're moving first. Neither effect is the reason to run this move.
Who runs it
Tyrantrum (16% usage) is the recorded carrier. It has Strong Jaw, which boosts bite and fang moves — Fire Fang included. That boost makes this legitimately powerful on Tyrantrum, not just a filler coverage slot. Dragon-type moves get resisted by Steel, and Rock-type moves aren't super effective on Steel either. Fire Fang fills that gap — and with Strong Jaw behind it, the damage is real enough to threaten Steel-type targets.
How to use it
You click this against Steel-type targets when your Dragon and Rock moves hit a wall. That's the primary use case: Tyrantrum switches in, the opponent brings in a Steel type thinking it walls you, and Fire Fang answers. In doubles, burn can apply pressure on physical attackers over multiple turns — chip damage adds up faster in the shorter game.
Tips & strategy
Don't plan around the secondary effects. Both burn and flinch are low-probability, and building a gameplan around them triggering is asking for variance to go the wrong way. The reason Fire Fang is on the set is Steel coverage amplified by Strong Jaw — the secondaries are bonuses, not the point.
If burn does land, it stacks with end-of-turn chip from other sources like Leech Seed or weather damage. A burned physical attacker under Sandstorm is taking meaningful HP loss every turn and hitting noticeably softer.