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.
Beat the game (any ending)
Activated and destroyed eight simultaneous Eggmins during Metallic Madness Zone Act 2
Defeated a Rexon with the Walker Legs in Lava Reef Zone
Found the secret submarine in Oil Ocean Zone Act 2
Found the hidden room in Press Garden Zone and destroyed all breakable crates as Sonic
Uncovered two item boxes with a single Goal Plate
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
Had Shutterbug take 10 photos
Burnt a log bridge in Green Hill Zone
Spun a Star Post 10 times by going fast
Collect gold medallions in Blue Spheres Bonus stage
Collect silver medallions in Blue Spheres Bonus stage
Collect all seven Chaos Emeralds
Try for a 3 chain combo!
Get through Stardust Speedway Zone as quickly as possible
That elusive perfect run, only a professional can achieve