Full list of all 18 Sonic Mania achievements worth 1,000 gamerscore. It takes around 15-20 hours to unlock all of the achievements on Xbox One.
Found the secret submarine in Oil Ocean Zone Act 2
Found the barrel that leads to a Special Ring in Mirage Saloon Zone Act 2
Uncovered two item boxes with a single Goal Plate
Activated and destroyed eight simultaneous Eggmins during Metallic Madness Zone Act 2
Got to the Stardust Speedway Zone Act 2 tower in under a minute
Flown through a ship window in Flying Battery Zone Act 2
Got a 3 chain combo in Chemical Plant Act 2 or in Mean Bean mode
Found the hidden room in Press Garden Zone and destroyed all breakable crates as Sonic
Had Shutterbug take 10 photos
Burnt a log bridge in Green Hill Zone
Beat Titanic Monarch Zone Act 1 without taking a single hit
Beat the game (any ending)
Defeated a Rexon with the Walker Legs in Lava Reef Zone
Collected all gold medallions in Bonus stage
Collected all silver medallions in Bonus stage
Found and rode all the boats in Hydrocity Zone Act 1
Spun a Star Post 10 times by going fast
Collected all seven Chaos Emeralds