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.
Collected all gold medallions in Bonus stage
Collected all silver medallions in Bonus stage
Beat Titanic Monarch Zone Act 1 without taking a single hit
Got a 3 chain combo in Chemical Plant Act 2 or in Mean Bean mode
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
Found the hidden room in Press Garden Zone and destroyed all breakable crates as Sonic
Flown through a ship window in Flying Battery Zone Act 2
Found and rode all the boats in Hydrocity Zone Act 1
Found the barrel that leads to a Special Ring in Mirage Saloon Zone Act 2
Found the secret submarine in Oil Ocean Zone Act 2
Collected all seven Chaos Emeralds
Uncovered two item boxes with a single Goal Plate
Beat the game (any ending)
Defeated a Rexon with the Walker Legs in Lava Reef Zone
Had Shutterbug take 10 photos
Spun a Star Post 10 times by going fast
Burnt a log bridge in Green Hill Zone