Here is the full list of all 20 Timberman achievements.
Unlock at least 4 out of 5 new steam exclusive characters
Win 33 4 players matches
Defeat 25 people by being much faster in 4 players mode
Beat 10 much stronger opponents in multiplayer
score 555 or chop 55555
Score 500 or chop 30000
Score 700 or chop 100000
Score 1001 or chop 150000
Fight 10 times in multiplayer mode
Win three rounds in a row by being much faster than opponent
Fight in multiplayer with devils and angles only
Defeat 5 different people in multiplayer
Score more than 200 three times in a row
Chop 200 logs in over 46 seconds in a single player game
Score 250 or chop 3917
chop 100 logs in 15 seconds
Launch the game 9 times
Let yourself be killed by branch with score 180 points exactly
Score 150 or chop 1117
Chop 10 logs in 2 seconds