Here is the full list of all 15 Paunch achievements.
Invite a friend for sparring
Get a six-win streak
Get a three-win streak
Strike the first counterblow
Win the first time
Begin scoring for the first time
Hit opponent one thousand times
Pick up one million boulders
Strike one thousand counterblows
Begin scoring one thousand times
Win 65 times
Win 90 times w/o empty boulder
Win 270 times w/o empty boulder
Get a nine-win streak
Accept invitations for sparring 365 times