i unlocked the periwinkle knight, barbarian, theif, gray knight, royal guard and some other character i dont know the name to. i also got troll, giraffey (you gotta dig him up somewhere in the desert) scratchpaw, rammy i think? the snail one, again, i forget the name, cardinal and thats all i unlocked. you get the royal guard by beating the story with the green knight. and you unlock the barbarian, thief and periwinkle knight by doing the first arena, the thieves arena and the volcano arena. for troll and scratchpaw i believe you need bombs, scratchpaw does for sure.
Edit: and i also got bitey bat owlet and seahorse im proabably missing a few others but i think you get my point