Clear Body is an Ability introduced in Generation III.
Clear Body prevents stat reduction caused by other Pokémon's moves and Abilities (such as Scary Face and Intimidate), including Sticky Web. Clear Body does not prevent self-inflicted stat reductions such as from moves like Superpower or Shell Smash.
Clear Body only protects from effects that lower stat stages, so it does not prevent stat reduction from items like the Iron Ball, the status conditions paralysis or burn, or the moves Guard Split or Power Split.
Outside of battle
Clear Body has no effect outside of battle.