Here is the full list of all 12 Kings And Goblins achievements.
Collect all 250 diamonds on first level
Kill all 54 goblins on first level
Collect all 250 diamonds on second level
Kill all 84 goblins on second level
Collect all 350 diamonds on third level
Kill all 148 goblins on third level
Die once on any level
Finish all 3 levels of Kings And Goblins on Normal game mode
Complete Kings And Goblins on Hardcore game mode
Complete Kings And Goblins on Speedrun game mode in less than 10 minutes
Finish all 3 levels of Kings And Goblins without killing any goblin on any game mode
Obtain all achievements