(I'm gonna have to type long)
I used a klefki (sub, iron defense, calm mind, and draining kiss) to sweep arven, try not to send out the klefki first because of greedent, scovillian, and toedscruel.
But for you, Gardevoir can die to Toedscuel (Sludge Bomb), maybe you can save gardevoir for mabosstiff.
Altaria can die to Garganacl, Mabosstiff (Play Rough) and Cloyster. Though you can try send out Altaria to get rid of Greedent, Toedscruel, and Scorvillian.
Mabosstiff can die to Arven's Mabosstiff (Play Rough) but you can still get tera type to a fairy.
Dondozo die to Scorvillian, Toedscruel, Geedent (Bullet Seed). You can try to get rid of gargancl.
Meowscaracade is dead to mabosstiff(Play Rough), Toedscruel (Sludge Bomb), and Scorvillian. You can try to get rid of Gargancl and Cloyster just be careful with cloyster.