Defensive Mega Bro (Slowbro-Mega) @ Slowbronite  
Ability: Shell Armor  
Level: 50  
EVs: 252 HP / 252 Def / 4 SpD  
Bold Nature  
IVs: 0 Atk  
- Slack Off  
- Ice Beam  
- Scald / Surf 
- Fire Blast / Iron Defence / Flamethrower
Surf can be used over scald with 12 spa evs to guarantee KO on mega blaziken, Iron defence is for bulky mega salamence or can add coverage for ferrothorn. 252hp/100spdef will allow you to live Charizard Y solar beam

OTR Mega Bro (Slowbro-Mega) @ Slowbronite  
Ability: Shell Armor  
Level: 50  
EVs: 252 HP / 252 SpA / 4 SpD  
Quiet Nature  
IVs: 0 Atk / 0 Spe  
- Trick Room  
- Scald / Surf 
- Ice Beam  
- Fire Blast / Psychic / Flamethrower
Similar to Porygon2 in a sense, OTR aims to just go in with mega bros spa and slow speed under the rooms. You can use psychic for coverage for toxapex, gengar, naganadel, venusaur and kommo-o under rooms.