Leavanny @ Choice Scarf
Ability: Swarm
EVs: 168 HP / 252 Atk / 88 Spe
Adamant Nature
- Leaf Blade
- X-Scissor
- Knock Off
- Aerial Ace
Voila, counter to both Heliolisk and Virizion. Only thing I could find that counters both, no matter what move they run, except for 4× effective Hidden Power.
EV'd to outspeed Sneasel as well as tank Virizion's Stone Edge, allowing for either Life Orb or Stealth Rock but not both.
Same for Heliolisk's Hyper Voice; it allows for Life Orb / Specs, or Stealth Rock, but not both of these.
Adamant nature to increase the chances of OHKO'ing Virizion with Aerial Ace and Heliolisk with Leaf Blade, respectively, but you need a bit of prior damage - 2% for Virizion and 6% for Heliolisk - to ensure these OHKO's.
It isn't a full counter though, but is certainly a very solid check that can repeatedly scare them out and if worst comes to worst switch into them (assuming hazards didn't wear it down too much). Kinda annoying Leavanny is weak to Rock, if it wasn't it would be so much better. Not even for SR - it is just that so many things it want to check/counter can carry Stone Edge...
Sawk @ Choice Scarf
Ability: Mold Braker
EVs: 112 HP / 252 Atk / 144 Spe
Adamant Nature
- Close Combat
- Stone Edge
- Ice Punch
- Poison Jab
EV'd similar to Leavanny; to outspeed Sneasel, remaining EV's put into HP to ensure it survives a STAB move from Heliolisk after SR, as well as Virizion's Life Orb Focus Blast. Just like Leavanny, it can tank any coverage move from both Virizion and Heliolisk (and this time, it includes Hidden Power). It is kinda obvious that Close Combat is far more spammable than a non-STAB Aerial Ace. Why isn't this mentioned first opposed to Leavanny, you ask? Because it needs SR and one layer of Spikes (16% prior damage) to ensure the OHKO Virizion with Close Combat, whereas Leavanny only need 2% of prior damage to do the same with Aerial Ace. However, non-STAB Aerial Ace means Leavanny will be set-up bait after revenging Virizion, which isn't the case as much with Sawk, using a 120 BP STAB move.
Also note that Sawk generally takes more from the STAB moves from either of these mons (even though it survives them easier), as well as coverage moves, because it has less resistances and slightly less overall bulk, but it also has less weaknesses, so it isn't going to be bopped by a random Hidden Power, whereas Leavanny can switch into the resisted STAB moves repeatedly (note that Leavanny doesn't like switching into a Volt Switch either, for obvious reasons).
Both can counter once or check repeatedly. You might want to shove more EVs into Speed, but then you can't counter once anymore ^ .
Note: I don't give a f*ck about how well these do in the current meta (especially with these EVs, lol). I just saw Virizion and Heliolisk, and wanted to come up with things that could counter either of them at least once in a match, and as such check both, which wasn't easy with the extensive coverage from Heliolisk and the mixed prowess of Virizion.
Edit: I also did not account for the possibility for Heliolisk or Virizion to run Scarf themselves. For both of them it'd be a waste though, since they are fast enough to begin with and they waste their potential when doing so.