I now there is a JASS trigger for this...but i can not write JASS only barely read it wanna make a spell that everytime u activate the ability it vhanges your attack to a random attacktype im not sure if tis is possible but help if u can
Simply create a self targetable innerfire which makes your attack -100% so you have no attack. Then when it is cast turn on a trigger that with the duriation of the bluff that when the unit attacks the target and dameges it 0 then deal (create a forrmular to culculate what the damage would be) damage of a random damage type.
I agree with purple pot, since super goods way is way to circumstantially, first of all the calculating of the damage and then the problem what if some1 dispells the inner fire effect. lol