Here is the full list of all 24 Mega Man Legacy Collection achievements worth 1,000 gamerscore.
Completed all six Mega Man games.
Unmasked Mr. X and completed Mega Man 6.
Discovered the truth about Proto Man and completed Mega Man 5.
Escaped the Skull Castle and completed Mega Man 4.
Turned Gamma to scrap metal and completed Mega Man 3.
Took out the Alien and completed Mega Man 2.
Completed the "ALL ROBOT RUSH (NO ITEMS)" Challenge.
Earned 50 gold medals by completing Challenges.
Earned 50 silver medals by completing Challenges.
Earned 50 bronze medals by completing Challenges.
Completed the "ALL ROBOT RUSH" Challenge.
Completed any Challenge marked with "NO ITEMS."
Completed the Dr. Wily Forever Challenge.
Completed the "ALL APPEARING BLOCKS" Challenge.
Earned 25 gold medals by completing Challenges.
Earned 25 silver medals by completing Challenges.
Earned 25 bronze medals by completing Challenges.
Stopped Dr. Wily's plans and completed the original Mega Man.
Earned 10 gold medals by completing Challenges.
Earned 10 silver medals by completing Challenges.
Earned 10 bronze medals by completing Challenges.
Earned 1 silver medal by completing a Challenge.
Earned 1 gold medal by completing a Challenge.
Earned 1 bronze medal by completing a Challenge.