If he subs on a counter switch in then he lost 25% hp he won't regain ever again (that+ Rocks damage chipping it) unless he wants to sacrifice a moveslot for Roost and that'd mean either losing Quake or SD.
If he SDs while his sub is being broken then he'll die the following turn unless said counter is chipped enough.
Toxic Gliscor is good vs P2 and Gligar but they aren't really rendered useless by it., toxic also means he's completely hopeless vs other pokemon.