This guy is notably good with weather, he can be built very well for either Rain or Sunshine weathers, I have 2 Sets for him, one for Sunny Weather and other for Rainy weather.
Sun Weather Sweeper
Heliolisk @ Choice Specs
Ability: Solar Power
EVs: 4 HP / 252 SpA / 252 Spe
Modest Nature / Timid Nature
- Thunderbolt
- Dark Pulse
- Focus Blast
- Hidden Power [Ice]
Thunderbolt is his STAB. Dark Pulse and Focus Blast are for coverage. HP [Ice] covers his Ground weakness and makes him able to deal with Dragons. The strategy here is to put this guy after someone set-up Sunny Day (or maybe Drought if you're using Groudon / Primal Groudon), ideally this Pokemon would set up Sunny Day, put up a Substitute for Heliolisk and then Batton Pass him some stat boosts (preferably SpA and Spe so he can sweep).
After the Baton Pass he has a defense, then you'll have 50% extra SpA from Solar Power and 50% extra SpA from Choice Specs, it literally doubles your SpA with these two (If I'm not mistaken it doubles the total ammount, not the Base ammount, so even better), with a Modest Nature, you're almost hitting 700 SpA, imagine this guy getting a stat buff along this? And he would have a Substitute so he could faint 2-3 guys before they actually manage to take him down. This just sounds too good to pass up for me. The only problem I can see is that he has subpar Physical Bulk and his Base HP is Extra Low, but with a Substitute and maybe a Taunter alongside him he can be pretty durable.
Rain Weather Sweeper
Heliolisk @ Choice Specs / Life Orb
Ability: Dry Skin
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Thunder
- Signal Beam / Agility
- Focus Blast
- Hidden Power [Ice]
Thunder is STAB, higher Base Power than Thunderbolt and since he's in a Rain Weather comp it is a realiable damage source. Signal Beam and Focus Blast for coverage, go with Agility if you went for Life Orb. HP [Ice] is the same deal as before. This guy has less SpA than Sun Heliolisk but he is a little bit sturdier because of his healing from Rain/Water Type moves, the concept is kinda the same here, though a bit simpler since he does not need a Batton Pass/Substitute to start Sweeping, he just needs someone to provide him with a Rain weather.
I put both together because I don't really care about upvotes/downvotes, since it's much easier to know what people didn't like about the set if they tell me rather than if they downvote me, simply downvotting won't say to me what specificaly is bad about my set.