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