How to Get Mega Gengar in Pokémon Legends: Z-A – Evolution and Location Guide
via screenrant.com
Short excerpt below. Read at the original source.
Pokémon Legends: Z-A is once again tasking players with hunting for precious stones, but in true Pokémon fashion, not all of them do the same thing. While there are evolution stones (as is customary since the first generation), there’s also individual Mega stones, which became a key mechanic in later Pokémon entries.