As in her legend, subjects caught in her vision will be unconditionally petrified if their Mana rank is C or lower, while those of B rank will be petrified depending on the result of saving throw.
I mean, why I wouldn’t say she could take out the entire army, let’s not forget she went toe-to-toe with Saber Alter who at the time was being powered by the grail and as far as we know, Iskandar commands minor Heroic Spirits.
So it’s not exactly out of the question but then again, she has a better chance at simply petrifying Iskandar before he launches his NP.
She can literally petrify all of them because the soldiers in his army are well …just normal soldiers with no innate magic resistance so I don’t think Ionioi Hetairoi is actually useful here.
Also it’s extremely in character for Medusa to use her Mystic eyes in any scenario she feels she is at a disadvantage.
About Iskandar’s other NP Gordius wheel, I would say Bellerophon should be able to destroy it pretty easily when we assume Gordius wheel was annihilated by Excalibur while Bellerophon could contest against Excalibur with some assistance from Shirou in HF.
In close combat Iskandar can’t keep up with Rider’s speed and he loses.
Having remained since the Age of Gods, its abilities are far beyond those of a normal Pegasus that would only be limited to the strength of a several hundred years old Monstrous Beast had it been one of the few remaining Phantasmal Species from the current age. Increasing in strength as it has lived, it has the strength of a Phantasmal Beast far beyond something like Invisible Air that could defeat a normal Pegasus.
Its strength is nearing that of the level of dragons, the strongest of the Phantasmal Species, and its defense has already reached that level. It is made of enough energy to have come from several hundred magi, and constantly emits it while it flies. It is a divine mystery with magical protection even greater than that of Artoria, who displays the strongest resistance of the Fifth Holy Grail War, allowing it to easily brush past all thaumaturgy without issue. Not needing to halt its charge against anything, it is much like a giant castle wall crashing down on the opponent and leaving them no method of dodging or defending.
I think Iskandar has too many disadvantages to win this one and you all are seriously underestimating Medusa and Bellerophon.
Iskander’s reality marble is greatly overestimated imo. Sure he summons an army of heroic spirits but what noble phantasms or skills do those servants have? If they don’t have any than they’re just strong dudes most other servants make their legends from killing. It’s EX ranked but the only servant he killed with it was hundred face hassan who isn’t meant for fighting in the first place and even with his chariot he was only able to stall Gilles’ giant monster when Excalibur one shots it and the chariot in a later battle.
Medusa at full power can stall Saber Alter (who should be much stronger than normal Saber with Kiritsugu) with near infinite mana in single combat through speed, her eyes and skill and with a little help from Shirou was able to overpower Excalibur Morgan (which should be significantly stronger or at least on par with a normal Excalibur) with Bellerophon. This is the same Saber Alter who casually fight Hercules earlier in HF. And as said her Mystic Eyes when unleashed would just stop Iskander and his army dead in their tracks since not even Iskander himself has enough mana to resist it. HF also shows that closing your eyes doesn’t work to prevent petrification. Also every time we see Iskander summon his army he’s at the front charging towards his enemy. If he would position himself like this to fight someone as weak as Hassan or as strong as Gilgamesh he would likely do the same to Medusa and get stoned or run over by her pegasus. Once he’s gone there isn’t much his army of strong dudes can do against a woman who’s been killing people like them for most of her life on the shapeless isle.