This is a pretty interesting idea!  I am always interested to see how people balance luck in their games, and I think you did a pretty good job with that here.  I read in the comments that having multiple rolls was a bug, so I tried playing with only one roll's worth of dice per turn and I found the difficulty to be just right.  The only major criticism I have about the gameplay is the the mirror enemies are unnecessarily tanky and tedious to fight - maybe they should take full damage instead of half while still reflecting damage onto the player?  I also noticed that getting an extra die is far more useful than increasing health, as the extra die can be used to heal far more than the additional starting health.  Other than that, the game is well made, and I had fun with it.  Congrats on finishing and submitting!

Also, I did run into the same bug as Danial, and it seems to happen whenever you drag one of the dice onto an object other than the player and enemies (like the end turn button).  I imagine you could fix it pretty easily by creating a parent object for the player and enemies and only having the dice react whenever it is dragged onto that parent object.

Its pretty easy I must say. While playing though, I experienced a crash: 

############################################################################################
FATAL ERROR in
action number 1
of Draw Event
for object obj_control:

Unable to find any instance for object index '100034' name '<undefined>'
at gml_Object_obj_control_Draw_0
############################################################################################
--------------------------------------------------------------------------------------------
stack frame is
gml_Object_obj_control_Draw_0 (line -1)

It seems way too easy.