Something to deal with Ground-types is absolutely necessary at this point. Yeah Clamperl can take them out, but we can't really switch into something like a Mudbray. As such, I'd like to propose:
Snivy @ Eviolite
Level: 5
Ability: Contrary
EVs: 240 SpA / 252 Spe
Timid Nature
- Leaf Storm
- Glare
- Synthesis
- Hidden Power Ice
Snivy provides us with a reliable switchin to these Ground-types, and thanks to Eviolite and Synthesis, it can keep doing it throughout the game. In addition, it can actually take significant advantage of them by getting a Contrary Leaf Storm boost. I say we go with Glare here since we already have 2 Knock Off users in Grimer-A and Pawniard, and paralysis spreading is nice. It also opens the way for Snubbull to run Heal Bell, since Snivy can spread paralysis. Snivy also benefits from Diggy trapping Pony/Larv. I went for HP Ice to hit Vullaby, which could otherwise be an issue.
If we go for Snivy, one big issue I see is the lack of VoltTurners to bring in Diggy and Clam, and lack of hazard removers to preserve Diggy's Sash. Defensive Vull could've done both of these things esp with it not needing Koff and a moveset of Roost/Brave Bird/U-turn/Defog being a possibility. I went with Snivy however, because Vullaby means we have no real way of switching into and actually taking out the likes of RestTalk Mudbray (also Snivy is much more fun to use imo).