Oh come on I am trying to make something that make sense concept-wise, not just brokeness for the sake of brokeness (also see: Lopunny). Mega mons gain a bonus of 100 stat points: put 30 in Atk to hit 195, and 70 in Spe to achieve a relevant speed tier of 128.
Give the guy a Steel sub-type (makes sense as its counterpart is Bastiodon) and the ability Rock Head (IMMENSELY fitting). Result: decent coverage, immense attack backed by good speed, still not broken because Mach Punch mauls it (Conkeldurr says hi).
