In battle
If a Pokémon with Thick Fat is attacked by an Ice- or Fire-type move, the opponent's Attack or Special Attack is reduced by 50% during damage calculation, effectively halving the damage the Pokémon takes.

Outside of battle
Thick Fat has no effect outside of battle.

During harsh sunlight, Leaf Guard prevents the Pokémon from being afflicted by non-volatile status conditions and Yawn (including via the Flame Orb and Toxic Orb). It has no effect on any current status condition prior to the weather being set up.

If a Pokémon with this Ability is drowsy due to Yawn, if there is harsh sunlight when it would fall asleep, the Ability activates and keeps it awake.

Outside of battle
Leaf Guard has no effect outside of battle.