Here is the full list of all 24 Best Buds vs Bad Guys achievements.
Achieved for completing downtown
Achieved for Spooky Graveyard
Achieved for completing Ancient Castle
Achieved for completing Bad Guy Training Camp
Achieved for completing Top Secret HQ
Achieved for completing Floating City of the Gods
Achieved for completing Toy World
Achieved for completing Ice Palace
Achieved for completing CandyWood
Achieved for completing Mushroom Village
Achieved for completing Hellish Factory
First teleport use
Blasting your first door with TNT bomb
Defeating your first boss
total play time over 2 hours
400 Jumps
100 Deaths
Collect all guns
Achieved for completing all levels
Achieved for completing all levels in game+
Achieved for shooting 100 enemies
Achieved for shooting 500 enemies
Retry 10 times in a row on the same level
Collect special gems from all levels