Mega Gengar is a Ghost / Poison‑type Pokémon, the same dual type as regular Gengar.

Type and resistances

  • Types: Ghost and Poison.
  • This means it takes reduced damage from Fighting‑type moves (thanks to Ghost) and from Poison‑type moves (thanks to Poison), but it is weak to Dark, Ground, Psychic, and Ghost‑type attacks.

Quick comparison table

[3][5] [9][5] [3] [3]
Pokémon Type Shared type with Mega Gengar?
Gengar (base) Ghost / Poison Yes
Mega Gengar Ghost / Poison Yes
Haunter Ghost / Poison Yes
Gastly Ghost / Poison Yes
So to answer directly: **Mega Gengar is a Ghost / Poison‑type** in every core series game and Pokémon GO where it appears.

Information gathered from public forums or data available on the internet and portrayed here.