This Coalossal already is planned to have Endure and Weakness Policy with Steam Engine as its Ability. I need to decide what the other 3 moves should be, but I can't. Coalossal has two 4× weaknesses and two 2× weaknesses, so this set needs to have some sort of coverage :D
Special Coalossal has a way better Physical movepool, but Scald covers more weaknesses.
Coalossal @ Weakness Policy Nature and EVs are whatever you want, but I recommend Modest nature and 252 SpA / 252 Spe / 4 Def Ability: Steam Engine -Endure -Ancient Power/Earth Power -Flamethrower -Scald
Scald covers Rock and Ground types.