The ghost-loving old lady leads with the same Pokémon: Arbok. This crafty snake can use Poison Jab, Crunch and Glare like before. Plus Earthquake to counter Steel-types trying to wall it. Psychic and Ground-types are strongly recommended to try and one-shot it before it can use Glare.
Agatha may send out her Level 63 Gengar next. It’s carrying the usual Shadow Ball, Sludge Bomb and Will-O-Wisp, along with a new move: Sucker Punch. A Dark-type special attacker is ideal, in case it uses Will-O-Wisp. It’s fast so there’s a good chance it’ll use it before you have time to react. Or you could sick Mega Mewtwo on it.
Golbat you should have a counter for, since you’re bound to have battled loads of these. This one can use Leech Life to hurt Psychic-types and steal their HP, on top of Air Slash, Crunch and Quick Attack. If in doubt, go with Electric or Rock-types.
Weezing is another Poison-type in place of a Ghost-type. It can use Fire Blast to counter Steel-types, in addition to its previous moveset of Sludge Bomb, Shadow Ball and Thunder (upgraded from Thunderbolt). Ground-types are still king, at least before it learns how to float.
Agatha’s Alolan import is the Fire and Ghost-type Marowak. This ominous creature can use Flare Blitz and Shadow Ball for STAB, although only the former is a real threat. Plus Bonemerang to hurt Rock-types, and Rock Slide because it ran out of ideas. Smite it with Water, Ground or Dark.
Lastly, Agatha’s second Gengar–the Level 64 one–can also use Sucker Punch just like the lower Level one. Its other moves remain the same: Shadow Ball, Sludge Bomb and Dazzling Gleam. Because it doesn’t carry Will-O-Wisp, you can safely field a Ground-type. Or continue pummeling it with Mega Mewtwo.