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