Pheromosa may be broken, but is not XY Mega Kangaskhan or Deoxys-N.
Deoxys-N had 150 Atk and SpA... and Psycho Boost, Superpower, Shadow Ball, Ice Beam, Thunderbolt, Screens, Stealth Rock, etc. I think it's way more dificult to deal with Deoxys-N than to this. And it isn't Deoxys-A.
High Jump Kick is inmune to Ghost (meaning it isn't spammable) and it's detrimental to use if someone has Protect and friends.
This list of Gen VI pokemon can check it:
-Clefable (Counter if not Poison Jab).
-AV Tornadus-Therian
-AV Heracross with Stone Edge or Mega Heracross with Rock Blast.
-Mega Sableye (Counter)
-Mega Slowbro.
-Talonflame (specially at full HP with Gale Wings).
-Thundurus (Paralyze).
-Azumarill (Hard check).
-Mega Pinsir
-Skarmory with Flying Attack.
-Ammonguss (can sleep it).
-Gengar (Hard check).
-Suicune (Crocune).
-Mega Venusaur (Counter).
-Mega Altaria (Hard check).
-Dragonite @ Extremespeed
-Intimidate Gyarados.
-Klefki with priority Thunder Wave.
-Volcarona (good Spin/Defog support, please).
-Kingdra in Rain.
-Togekiss
-Scolipede with Stone Edge.
And about new things:
-Aegislash (May be broken itself).
-M-Mawile (when GF wants).
-Primarina.
-Ribombee (highly unlikely to be viable).
-Toxapex (very good).
-Araquanid (this things has Water Bubble (×2!!!) BP STAB Liquidation (85 power) and good defenses).
-Silvally with Poison, Flying, Ghost or Fairy Memory. Maybe some of then are OU Viable.
-Mimikyu
-Tapu Koko (very good).
-Tapu Lele (one of his better allies could be one of his biggest enemies, and very good).
-Tapu Fini.
-And Shift Gear Magearna.!!!!
Not all of them are counters, but I think all of them are checks that can take standard Pheromosa at least decently. I found 40 checks to it... something overly broken doesn't have 40 potential checks, and more than half are OU viable right now.