Magma Armor prevents the Pokemon from being frozen.
A Pokemon with this Ability will be thawed out if it is frozen while in battle (such as if it gains the Ability outside of battle or by an effect like Skill Swap, or is frozen by a Pokemon with an Ability like Mold Breaker). If the Pokemon is holding anAspear Berry or a Lum Berry, it will be eaten before Magma Armor thaws out the Pokemon.
Outside of battle
If a frozen Pokemon gains Magma Armor by evolution or the Ability Capsule, it will not be thawed out until sent into battle. Pokemon with Magma Armor will not be frozen by the Gentleman’s Dusclops in the Battle Pike nor the Battle Arcade’s game board.
From Pokemon Emerald onward, Magma Armor halves the number of cycles it takes for all Pokemon Eggs in the party to hatch. This effect does not stack with itself nor Flame Body; however, it can be stacked with Hatching Power.
Pokemon with Magma Armor