My suggestion is
Toxicroak (M) @ Black Sludge
Trait: Dry Skin
EVs: 244 HP / 252 Def / 12 Spd
Impish Nature (+Def, -SAtk)
- Toxic
- Protect
- Substitute
- Drain Punch
Yes, thanks to Dry Skin and its poison typing, Toxicroak walls Keldeo completely even in rain. Another plus for Toxicroak is that it doesn't fear Tyranitar at all, though Landorus is a common partner for Keldeo that makes Toxicroak cower. Mandibuzz therefore makes a great partner to Toxicroak, it can take on Landorus very well (it avoids the 2HKO from Focus Blast 2/3rds of the time after Stealth Rock not counting accuracy, Hidden Power Ice does even less) while also taking on other pokemon that beat this set very well like Gengar, Jellicent, Reuniclus and both Magic Bounce pokemon. However, Drizzle Politoed is a required partner for this set to be effective so bear that in mind when choosing Toxicroak on your team.
Toxicroak (M) @ Black Sludge
Trait: Dry Skin
EVs: 244 HP / 252 Def / 12 Spd
Impish Nature (+Def, -SAtk)
- Toxic
- Protect
- Substitute
- Drain Punch
Yes, thanks to Dry Skin and its poison typing, Toxicroak walls Keldeo completely even in rain. Another plus for Toxicroak is that it doesn't fear Tyranitar at all, though Landorus is a common partner for Keldeo that makes Toxicroak cower. Mandibuzz therefore makes a great partner to Toxicroak, it can take on Landorus very well (it avoids the 2HKO from Focus Blast 2/3rds of the time after Stealth Rock not counting accuracy, Hidden Power Ice does even less) while also taking on other pokemon that beat this set very well like Gengar, Jellicent, Reuniclus and both Magic Bounce pokemon. However, Drizzle Politoed is a required partner for this set to be effective so bear that in mind when choosing Toxicroak on your team.









