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