Oh wow I wish I knew this. Haha, I even had a Gengar in my team but I just relied on switching and reviving with this team:
95 Salamence
95 Gengar
93 Kingdra
95 Staraptor
2 low level Sturdy Magnemites with Thunder Wave (super useful for paralyzing the super fast Mega Alakazam/Mega Salamence)
I didn't even use Gengar for Lance, haha, since Staraptor/Salamence had Intimidate it made them take hits better.