Here is the full list of all 33 Runner3 achievements.
Make it to the end of an Impossible Level!
Defeat Foodland's Boss!
Get a Perfect in each Standard Level in any World!
Checkpoints? Who needs 'em!
Get a Perfect+!
Get a Special!
Get a Special+!
Get a Special AND a Perfect in any one level!
Get a Special, a Perfect, and one Bullseye in any Level!
Get a Perfect!
Get a Special+ and a Perfect+ in any Level!
Collect all Golds and Gems and finish an Impossible Level!
Finish all 9 Impossible Levels!
Get a Special in each Standard Level in any World!
Head off the Beaten Path...
Got 'em All!
Get all the Gildans!
Witness something creepy.
Defeat Spookyland's Bosses!
Defeat Machineland's Boss!
Bonk the Timbletot!
Defeat The Great Outdoors' Boss!
Defeat The Caves' Bosses!
Defeat the Jungle Ruins' Boss!
Collect all the Narrator's Puppetshow Puppets!
Invite a friend to the BBQ!
Get all your friends over for some GRILLINS!
Better out than in...
Unlock EVERYTHING!
Buy a bunch of new digs!
Go exploring in the Retro World. Maybe you'll find a cute secret?
Buy a bunch of Accessories!
Buy a bunch of Capes!