Fumer

Only the RAMROD: one hit kills it; normal bullets do nothing

The white Molded. Normal weapons don't hurt it; a single RAMROD (Anti-Regen Ammo, switched in with ZL + X), ideally to the chest, kills it. Explosions or a hit after a block stun it. It gives off spores that drain your oxygen. Avoid it until you have RAMRODs; in the spore tunnels, running past it stays a good idea. A Neuro-stun Grenade also gets it off you. In the Shield Machine waves, keep a RAMROD loaded for the one in each wave.

10,000 HP (datamined; that source says it can be knifed to death, another that only the RAMROD hurts it). Normal: 13 (14 on Professional). Storage Area C1, C3, E2, N2 and S1: 1 each (the N2 one is the first you can kill); Repair Yard: 1 after the Clown Key; Work Sector A: 2 after the arm bomb; Mining Work Area Passage: 1; Shield Machine: 1 in wave 1 and 1 in wave 2; Experimentation Room: 2 by the bed.