This is the right place for the question. Toxicroak defensively ? I would say this:
@ Black Sludge:
Trait: Dry Skin
EV: 196 Speed / 252 Sp.Def / 64 HP
- Poison Jab
- Drain Punch
- Bulk Up
- Bullet Punch
So, here is a Bulk Up double set. Toxicroak makes a great use of Surf from an ally with Dry Skin, especially coming from Drizzletoad so that the weakness to fire given by Dry Skin is arranged. As for the moves, Bulk Up will make up for the lack of EV physically. Poison Jab is your premier STAB and an answer against fairies and grass. Drain Punch is for a concept: Drain Jab. Or Poison Punch. Or simply: The Drain-Poison system. Poison Jab has 30 % of chances to poison, while Drain Punch gives you back a healthy Toxicroak, alongside Dry Skin and Black Sludge. After, the last slot is an open choice, I prefer Bullet Punch for priority if Toxicroak is not enough quick to finish some nasty opponents. And the EV spread is would be the following:
196 Speed / 252 Sp.Def / 64 HP.
Hope I helped !