Flash Fire
Protects against Fire moves. Once one has been blocked, the Pokémon's own Fire moves inflict 1.5× damage until it leaves battle.
Full effect
This Pokémon is immune to Fire-type moves. Once this Pokémon has been hit by a Fire move, its own Fire moves will inflict 1.5× as much damage until it leaves battle. This ability has no effect while the Pokémon is frozen. The Fire damage bonus is retained even if the Pokémon is frozen and thawed or the ability is lost or disabled. Fire moves will ignore this Pokémon's Substitute. This ability takes effect even on non-damaging moves, i.e. Will-O-Wisp.
In game description
If hit by a Fire-type move, the Pokémon absorbs the flames and uses them to power up its own Fire-type moves.
Pokemon with Flash Fire
Vulpix
#0038
Ninetales
#0058
Growlithe
#0059
Arcanine
#0077
Ponyta
#0078
Rapidash
#0136
Flareon
#0155
Cyndaquil
hidden
#0156
Quilava
hidden
#0157
Typhlosion
hidden
#0228
Houndour
#0229
Houndoom
#0485
Heatran
#0607
Litwick
#0608
Lampent
#0609
Chandelure
#0631
Heatmor
#0837
Rolycoly
hidden
#0838
Carkol
hidden
#0839
Coalossal
hidden
#0850
Sizzlipede
#0851
Centiskorch
#0935
Charcadet
#0936
Armarouge
#0937
Ceruledge
Using Flash Fire in Cobblemon
Abilities are passive and always active, so Flash Fire costs you nothing to run. If it is marked hidden on a species above, expect it to be harder to obtain: servers differ in whether hidden abilities come from breeding, an Ability Patch, or events.
See the Pokedex for which abilities each species can have, and IVs, EVs and breeding for how to actually pass one down.