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.
Got all collectibles.
Cleared all the missions.
Got all custom skills.
Completed all of Sonic's friends' Challenges.
Cleared half the missions.
Cleared CHEMICAL PLANT without entering the water.
Cleared Green Hill within one minute.
Got Rank S in all acts.
Got all Red Star Rings.
Joined the rankings.
Participated in a 30 Second Trial.
Chatted with all of Sonic's friends you saved.
Got Rank S in acts 12 times.
Cleared Sonic Generations.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts seven times.
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 three times.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Defeated 100 enemies.
Got Rank S in an act.
Completed the first stage.