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