Here is the full list of all 49 Sonic Generations Collection achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Played Time Attack on all stages.
Took no damage while defeating the final boss.
Got all custom skills.
Cleared Sonic Generations.
Got all collectibles.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Cleared CHEMICAL PLANT without entering the water.
Got all Red Star Rings.
Chatted with all of Sonic's friends you saved.
Got Rank S in all acts.
Cleared half the missions.
Got Rank S in acts 12 times.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts seven times.
Cleared Green Hill within one minute.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Executed a trick with a seven-step combo or longer.
Participated in a 30 Second Trial.
Joined the rankings.
Defeated 100 enemies.
Got Rank S in acts three times.
Got Rank S in an act.
Completed the first stage.