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