Edit: Changed my counter because Camerupt is 2HKOed by Specs Eruption after a little bit of prior damage.
Clearly not the most obvious choice, but I think Grumpig is a pretty underrated mon.
The problem with most of Typhlosions common checks and counters is that if they are flash fire they are probably 2HKOed by Focus Blast, Seismitoad and Rhydon are bopped by HP Grass, Camerupt only needs some prior damage to be 2HKOed, and Dragalage and Hariyama are 2HKOed by Extrasensory with some prior damage.
I present to you, the 100% counter to all Typhlosion sets:
Grumpig @ Leftovers
Ability: Thick Fat
EVs: 248 HP / 8 SpA / 252 SpD
Calm Nature
- Thunder Wave / Toxic
- Heal Bell
- Psychic / Psychock
- Whirlwind / Signal Beam / Taunt / Whatever
Grumpig has a great Special Defense stat backed by an amazing ability in Thick Fat effectively giving it a resistance to Fire-type moves.
Calcs:
252 SpA Choice Specs Typhlosion Eruption (150 BP) vs. 252 HP / 252+ SpD Thick Fat Grumpig: 109-130 (29.9 - 35.7%) -- 38.5% chance to 3HKO after Stealth Rock and Leftovers recovery
252 SpA Choice Specs Blaze Typhlosion Fire Blast vs. 252 HP / 252+ SpD Thick Fat Grumpig: 121-144 (33.2 - 39.5%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
yumE. And in return, Grumpig can cripple it with a status move of choice, phase it out with whirlwind, or hit it with a STAB move.