Title? No Really

I return to this a few months later and can't figure out my own title. 64M3HO521

64M3 = Game?
643521 are the numbers on a d6?
51MO2 = Simon?
H521 = Hvnt?
3H from H3RNE?
MHO = Scale of hardness?

I have no idea... but I might just as well keep it...