Here is the full list of all 31 Oafmatch achievements.
Match five or more gems of the same color in a single match
Match six or more gems of the same color in a single match
Get three gold stars in every battle in Mendra Coast
Get three gold stars in every battle in Mendra Bay
Get three gold stars in every battle in Mendra Crags
Get three gold stars in every battle in Rayburn's Canyon
Get three gold stars in every battle in The Boneyard
Get three gold stars in every battle in Shear Valley
Get three gold stars in every battle in Agrinji's Pit
Get three gold stars in every battle in The Shuttered Depths
Triumph over the Unearth invasion of Mendra
Earn three gold stars in every campaign battle
Get a Brutal Combo
Get a Monster Combo
Get a Killer Combo
Kill three foes with a single attack
Complete Agrinji's Dungeon
Triumph over the Unearth invasion of Mendra in Campaign Plus mode
Escape alive from the Dungeon of the Dark God!
Slay Jaina Randall the Sorcerer
Slay Milo Randall the Sorcerer
Slay the Randall twins simultaneously, preventing either of them from ascending to Sorcererhood
Unlock all fifteen playable characters in the campaign
Unlock all thirty playable characters in a roguelike game
Learn about the history of the Old Sorcerers
Defeat the final boss with a full party of Strength characters
Defeat the final boss with a full party of Constitution characters
Defeat the final boss with a full party of Dexterity characters
Defeat the final boss with a full party of Intelligence characters
Defeat the final boss with a full party of Wisdom characters
Defeat the final boss with a full party of Charisma characters