>>15705763Don't. Best moves to pick from are:
-Return (best STAB you can get)
-Sucker Punch (priority)
-Crunch (no priority but good damage against Ghost types)
-Fake Out (personally wouldn't use it but it has its uses)
-Earthquake (good attack all around, extra coverage)
-Power-Up Punch (that attack boost)
You can look for other moves if you don't want to seem obvious. Thrash isn't recommended because you're giving Gengar a free switch-in.