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