O.S.C.A.R. is extremely tanky, slow-moving, looming threat patrolling the map. The only weapon that is effective against him is the LGM-1 when Pack-a-Punched. Spamming the drones on him will do significant single-target damage and will be your best chance. This is the type of enemy that you mainly want to avoid and ignore, similar to past enemies like the moon Astronaut Zombie or the George A. Romero.

The Drone Shield he summons around him though can be easily destroyed with a weapon with the Brain Rot ammo mod, as the drones around him are weak to that damage type. O.S.C.A.R. himself however, does not have any weaknesses to specific ammo mods.