Full Metal Body prevents stat reduction caused by other Pokémon's moves and Abilities (such as Scary Face and Intimidate), including Sticky Web. Full Metal Body does not prevent self-inflicted stat reductions such as from moves like Superpower or Shell Smash.
Full Metal 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. Full Metal Body does not prevent stat stages being directly modified by Haze, Clear Smog, Heart Swap, Guard Swap, Power Swap, Baton Pass, or Topsy-Turvy.
Unlike White Smoke and Clear Body, this Ability cannot be ignored by moves or Abilities.
Outside of battle
Full Metal Body has no effect outside of battle.