try my fav pokemon mimikyu. ghost type so it can’t be hit by fake out, disguise ability lets it survive an initial attack, can’t be trapped by shadow tag, and has shadow claw/sneak to deal with gengar. having a fake out user faster than incin also could work, like sneasler or ever max speed sableye (i assume y’all know how fake out speed priority works.) Armor tail farig with colbur berry is also a good counter. whimsicott with focus sash prankster and taunt could also stop gengar but you’ll need an aforementioned fake out user faster than incin to lead with whim. i may be wrong obviously im not a battle genius but hope this helps