In order to counter Cobalion you should look at what deck you're playing to see which part of Cobalion hurts the most.
If you're worried about Energy Press, try attaching your energy better, or play a ''sacrifical lamb'' while building up something for the sweep.
If you're worried about Iron Breaker (wether it be the 80 damage or the ''attack lock''), also play a ''sacrifical lamb'' to soak the damage and the ''attack lock'', and then counter attack when you're ready.
If you're worried about it tanking, try playing Lost Remover/Crushing Hammer. Removing the Sp. Metals will help you greatly, as well as setting back the Cobalion player a turn with it's manual energy attachments. Of course this won't help against the CaKE deck, but you could catch your opponent off guard.
In general, any fire type tech that can easily hit for 60 damage (when not factoring in Sp. Metals and/or Eviolite) is a good counter to Cobalion. I know I'm stating the obvious, so some examples are in place I guess (in terms of counters, I'll ignore Eviolite for now).
List of Fire type techs
- Reshiram (it requires 40 damage as well as 2 energy at a minimum to pull this off though)
- Typhlosion Prime (it can charge itself when needed and when playing the right energy type, and Cobalion needs 2 Sp. Metals to avoid the OHKO)
- Victini NV #15 (while it requires you to have 5 Benched Pokémon, and it will be revenge KO'ed quite easily, V Create is more than enough to take out any Cobalion (yes, even when loaded with Sp. Metals ánd an Eviolite attached!), the only thing that hinders Victini from being a truly ''good'' counter is it's meager 70HP.)
- Heatmor NV (''WHAT?! Heatmor?!'' Well, yes, Heatmor. While only doing 30 damage, Heatmor can get rid of those nasty Eviolites, as well as doing 60 damage. While Heatmor won't win you the game, it can sure prove to be a nuisance for Cobalion players who rely on their Eviolites too much)
- Simisear EP (can OHKO a Cobalion packing a single Sp. Metal energy for a fire energy and a DCE, at the cost of an energy discard)
- Simisear NV (can OHKO a Cobalion packing 2 Sp. Metal energy for 2 fire energy and somethign else, at the hopes of flipping at least 1 heads. Don't forget Fliptini can help out here too!)
- Simisear BW (can OHKO a Cobalion packing 2 Sp. Metal energy for 3 energy of any kind, and flipping at least 2 heads out of 3 flips. Once again, Fliptini can be quite helpful here)
- Darmanitan BW (for 1 fire energy and a DCE Darmanitan will OHKO Cobalion, even when packing a single Sp. Metal energy or an Eviolite. On a lucky flip you will OHKO it anyways (unless Cobalion packs some Defender), and on a tails the recoil won't matter that much. Fliptini can help you out here too)
- Emboar BW (both versions have enough attacking power to wipe Cobalion clean off the board. Do I need to say more?)
- Any fire type LEGEND (will outright destroy Cobalion, where SEL and ERL require some dedication, they both come with their own ''second trick'' in the form of power-nuking and sniping abillities, Ho-Oh LEGEND can work with anything you slap onto it (thanks to it's body), but any of these 3 will OHKO Cobalion)
Those are some counters I can think of, just see what appeals to you, and what might fit into your deck. If you have something like ''Hey, why isn't [insert card name here] on your list?'', then I probably couldn't think of it, or it just isn't enough to slice the CaKE (bad pun, sorry) in the competitive attacking format at all (a prime example is Houndoom prime, which should just sit on the bench in my opinion).
Finally I would like to say that Cobalion itself and Zoroark are your best bets to counter Cobalion if you're not looking at a Fire type counter (but this has been said already, so no need for me to go into detail here).
Good luck!!
