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.
Took no damage while defeating the final boss.
Cleared CHEMICAL PLANT without entering the water.
Cleared Green Hill within one minute.
Chatted with all of Sonic's friends you saved.
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.
Participated in a 30 Second Trial.
Played Time Attack on all stages.
Joined the rankings.
Cleared Sonic Generations.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got Rank S in all acts.
Cleared half the missions.
Got Rank S in acts 12 times.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts seven times.
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.