Skarmory, Corviknight, Rillaboom, Dondozo, Landorus-T, Bulky Serp, Sinistcha, Scizor and Barraskewda are a few
+2 252 Atk Tera Fighting Iron Boulder Close Combat vs. 252 HP / 160+ Def Skarmory: 223-264 (66.7 - 79%) -- guaranteed 2HKO (outdamages iron defense on switch-in)
+2 252 Atk Iron Boulder Mighty Cleave vs. 252 HP / 136+ Def Corviknight: 225-265 (56.2 - 66.2%) -- guaranteed 2HKO after Leftovers recovery
136+ Def Corviknight Body Press vs. 0 HP / 0 Def Iron Boulder: 90-107 (28 - 33.3%) -- 0% chance to 3HKO
252+ Atk Choice Band Rillaboom Grassy Glide vs. 0 HP / 0 Def Tera Fighting Iron Boulder in Grassy Terrain: 228-268 (71 - 83.4%) -- guaranteed 2HKO after 1 layer of Spikes and Grassy Terrain recovery
+2 252 Atk Tera Fighting Iron Boulder Mighty Cleave vs. 0 HP / 4 Def Rillaboom: 319-376 (93.5 - 110.2%) -- guaranteed OHKO after Stealth Rock
+2 252 Atk Tera Fighting Iron Boulder Close Combat vs. 252 HP / 4 Def Serperior: 385-454 (108.7 - 128.2%) -- guaranteed OHKO
0 SpA Serperior Leaf Storm vs. 0 HP / 4 SpD Iron Boulder: 206-246 (64.1 - 76.6%) -- guaranteed 2HKO
+2 252 Atk Tera Fighting Iron Boulder Mighty Cleave vs. 76 HP / 0 Def Scizor: 294-346 (98 - 115.3%) -- 87.5% chance to OHKO
252+ Atk Choice Band Technician Tera Steel Scizor Bullet Punch vs. 0 HP / 0 Def Tera Fighting Iron Boulder: 260-306 (80.9 - 95.3%) -- guaranteed 2HKO
it's checked by all this stuff, in a non-tera metagame, with an asterick. At the very least it trades with a lot
oh and to raikoulover:
+4 252 Atk Tera Fighting Iron Boulder Close Combat vs. 252 HP / 0 Def Great Tusk: 441-519 (101.6 - 119.5%) -- guaranteed OHKO
4 Atk Great Tusk Headlong Rush vs. 0 HP / 0 Def Tera Fighting Iron Boulder: 196-232 (61 - 72.2%) -- guaranteed 2HKO
have I mentioned that I dislike tera yet?