I like the core mechanic and the fact the runes are randomly generated. It would be nice if the skeleton gave you another set of runes after completing the first set. Maybe also make it so you can only get so many wrong, or there is a time limit and each wrong guess reduces your time, and you only get more time by clearing a set. That way you could have some levels and progression while keeping the fun central mechanic. I really enjoyed it, good job!