Where to catch Muk

In Blueberry Academy (Scarlet & Violet – The Indigo Disk)

• Coastal Biome — Walk, Static Encounter
• Torchlit Labyrinth — Walk

In Johto & Kanto (Gold, Silver & Crystal)

• Celadon City — Surf
• Route 16 — Surf, Walk
• Route 17 — Surf, Walk
• Route 18 — Surf, Walk

In Kanto (Red, Blue & Yellow)

• Cinnabar Island — Walk
• Kanto Power Plant — Walk
• Pokémon Mansion — Walk

Muk — full Pokédex entry