Ser Gregor Clegane of House Clegane, The Mountain that Rides, has been transported from his world (raised from the dead and returned to peak capabilities in the process) to appear before the council of a mysterious group calling themselves the Ourea.
It seems that news of his feats and exploits have reached the Ourea, and- believing him uniquely suited for their purposes- have deigned to make him the following offer:
Deal with those who have violated the sanctity of the mountains over which they preside, and be rewarded with anything he desires. To be more specific, for every individual in fiction which has destroyed or otherwise ruined a mountain that Ser Gregor Clegane defeats, he gets one wish1 of his granted.
Of course, as mighty as The Mountain is, he obviously would have no chance in a fight against any true mountain destroyer, so the Ourea- for the duration of this quest- will imbue The Mountain with the True Spirit of the Mountains2 in order to allow him to fight- and hopefully defeat- the Ourea's hated enemies for their crimes against mountain-kind.
How well does The Mountain, imbued with the True Spirit of the Mountains, do against actual mountain busters? Let's assume that The Mountain in question is:
- The Mountain of A Song of Ice and Fire
- The Mountain of Game of Thrones
- Real world Conan Stevens
- Real world Ian Whyte
- Real world Hafþór Júlíus Björnsson
1Wishes are at a minimum strong enough to do anything explicitly listed in 5e D&D's Wish spell description. If a wish is beyond the Ourea's ability to grant, it doesn't waste a wish.
2Essentially, The Mountain gets the stacked stats of a mountain's weight worth of himself. If someone actually has good estimates on an actual mountain's weight for calculation purposes, that would be neat; otherwise for laziness sake, assume this is a stacked composite of 1 trillion of the particular individual character in question. Every relevant stat for The Mountain is multiplied by 1 trillion (or whatever the actual calculation is) except for movement speed and reaction time, which are only multiplied by 1 million (or the square root of said actual calculation).