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