Here are five:
-defeat ten enemies as gatherer or crafter (or achievement for each class)
-survive a powerful ability with one HP left (holmgang probably best way to get it OR it doesn't count)
-defeat any HM primal with only four players (take a team to take turns with and the original four have to not do anything, or the could be a specific duty to select)
-defeat turn 2 with each combination of buffs and enrage method (adding this achievement will mean they don't have to get rid of enrage method)
-defeat turn four without attacking anything until phase 4.