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