cant say
Regirock is a beast, and in this case, a counter for Talonflame.
Mono Rock typing is also nice, which removes the possibility of having to take a 4x effective Natural Gift at +2 (although the Natural Gift set is quite rare).
Even with 0 def investment an adamant +2 salac berry Talonflame will fail to do more than 65%, and will get KO’d in return.
Ice Punch has a high chance to OHKO SR Garchomp and OHKOs Lando-T (if coming in after Intimidate).
Now the REAL beauty with this thing is the ability to check BOTH Charizard, both X and Y.
Thanks to Assault Vest Regirock can shut down those who like to lead with Charizard.
Calcs
+2 252+ Atk Salac Berry Talonflame Natural Gift (100 BP Fighting) vs. 252 HP / 0 Def Regirock: 102-120 (54.5 - 64.1%) -- guaranteed 2HKO
252+ Atk Regirock Ice Punch vs. 0 HP / 4 Def Garchomp: 164-196 (89.6 - 107.1%) -- 43.8% chance to OHKO
252+ Atk Regirock Ice Punch vs. 0 HP / 4 Def Landorus-T: 172-204 (104.8 - 124.3%) -- guaranteed OHKO
Sword Dance + Flame Charge Adamant Zard X
+2 252+ Atk Charizard Outrage vs. 252 HP / 0 Def Regirock: 62-73 (33.1 - 39%) -- 99.8% chance to 3HKO
+2 252+ Atk Charizard Earthquake vs. 252 HP / 0 Def Regirock: 102-122 (54.5 - 65.2%) -- guaranteed 2HKO
Modest Zard Y
252+ SpA Mega Charizard Y Solar Beam vs. 252 HP / 4 SpD Assault Vest Regirock: 116-138 (62 - 73.7%) -- guaranteed 2HKO