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