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.
Got all collectibles.
Got all custom skills.
Got all Red Star Rings.
Cleared Green Hill within one minute.
Cleared CHEMICAL PLANT without entering the water.
Got Rank S in all acts.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got Rank S in acts 12 times.
Performed all of Sonic's actions in Act 2.
Cleared half the missions.
Got Rank S in acts seven times.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Chatted with all of Sonic's friends you saved.
Participated in a 30 Second Trial.
Joined the rankings.
Cleared Sonic Generations.
Executed a trick with a seven-step combo or longer.
Defeated 100 enemies.
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.
Played Time Attack on all stages.