Where to catch Haunter

In Paldea (Scarlet & Violet)

• Dalizapa Passage — Walk
• Glaseado Mountain — Walk
• Levincia — Trade
• North Province (Area One) — Walk
• West Province (Area One) — Walk

In Kitakami (Scarlet & Violet – The Teal Mask)

• Mossfell Confluence — Walk
• Oni Mountain — Walk

In Johto & Kanto (Gold, Silver & Crystal)

• Rock Tunnel — Walk
• Route 8 — Walk

In Kanto (Red, Blue & Yellow)

• Pokémon Tower — Walk

Haunter — full Pokédex entry