Here is the full list of all 21 Mega Man Legacy Collection 2 achievements.
Liberate Dr. Light and complete Mega Man 9.
Prove yourself stronger than Bass and complete Mega Man 7.
Eliminate the Evil Energy and complete Mega Man 8.
Use Proto Man to liberate Dr. Light and complete Mega Man 9.
Cure the Roboenza and complete Mega Man 10.
Use Proto Man to cure the Roboenza and complete Mega Man 10.
Use Bass to cure the Roboenza and complete Mega Man 10.
Earn 1 bronze medal by completing a challenge.
Earn 10 bronze medals by completing challenges.
Earn 25 bronze medals by completing challenges.
Earn 1 silver medal by completing a challenge.
Earn 10 silver medals by completing challenges.
Earn 25 silver medals by completing challenges.
Earn 1 gold medal by completing a challenge.
Earn 10 gold medals by completing challenges.
Earn 25 gold medals by completing challenges.
Earn 50 gold medals by completing challenges.
Complete the "BOSS RUSH" challenge (Mega Man 7).
Complete the "BOSS RUSH" challenge (Mega Man 8).
Complete the "BOSS RUSH" challenge (Mega Man 9).
Complete the "BOSS RUSH" challenge (Mega Man 10).