How to evolve Gastly in Cobblemon.
Gastly evolves into Haunter when it reaches level 25.
Evolution line
GastlyWhat Gastly needs
1 path
HaunterLevel up
Level 25
Moves it learns on evolving
Shadow Punch
These are offered the moment the evolution completes. Decline them and you have to relearn them later.
Is it worth it
Gastly nowghostpoison310
Haunterghostpoison405
Base stat totals, from the Cobblemon 1.7.3 species files.