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