Rampardos's attack's damage isn't affected by Resistance, Poké-Powers, Poké-Bodies, or any other effects on the Defending Pokémon.

Head Smash80

If the Defending Pokémon would be Knocked Out by this attack, Rampardos does 40 damage to itself.

Mold Breaker40

Any damage done to Rampardos by attacks is reduced by 20 (after applying Weakness and Resistance) until the end of your next turn.