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