Judging by that,I assume you already have a mythical torso.
If that’s so,I think you should go with either an energy-free side (Mercy or Annihilation) or the Rolling Beasts.
However,if you wanna scare people off and force them to stay in closer range,go for the Flaming Scope.You’ll get more close-combat with it.
What would I choose from all those for my own mech?
You have a heat drone on a phys build?
Well,that would work a little better against energy builds…Tho you’ll get less phys res drain on every fight,not just on those against energy types…