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