Here is the full list of all 35 Beeftacular achievements.
Complete 100 speedruns
Complete a speedrun
Publish 15 nice custom levels in the Steam Workshop
Create 10 custom levels
Create a big custom level
Create a nice, custom level in the editor
Complete 100 custom levels that were created by other players
Do three double kills in one level
Do a ranged triple kill
Finish all 90 official classic levels
Get more than 10 ranged kills in one level
Get cut in half by a crossbow bolt
Kill a target by shooting a projectile through a portal
Jump through a laserbeam where you can still feel the heat
Finish the first 45 official classic levels
Be fast
High speed crash against a wall
Complete a secret level
Less than one second difference to the current world record
Find a secret in a level
Complete 10 custom levels that were created by other players
Play a custom level
Kill a target in front and back of you in one jump
Die and ragequit
Destroy a destructible wall using your body only
Kill a target using a falling wall
Kill a target that is not on screen
Do more than 15 consecutive walljumps
Complete a level with less than a second of time left
Do a ranged double kill
Kill a target using a projectile while falling
Kill all targets of a level using projectiles only
Get a time over
Take an interested look at the credits
Play for 2 hours straight