- Earn Mega Energy by walking with your Buddy Pokémon if you have previously Mega Evolved a Pokémon in your Buddy Pokémon’s Evolutionary line.
- Earn additional Candies when you have an active Mega-Evolved Pokémon and you catch a Pokémon that shares a type with your Mega-Evolved Pokémon. You will also earn additional Candies when catching a Raid Boss, regardless of its type.
- See Trainers on your friend list who currently have a Mega-Evolved Pokémon.
- Earn 15 Mega Energy every time you receive a Candy from walking with a Buddy Pokémon that is capable of Mega Evolving in Pokémon GO.
- Earn five Mega Energy for Mega Beedrill and and five Mega Energy for Mega Pidgeot using the same procedure.
Source: Official Pokémon GO blog