Metagross is one of the most powerful non-Legendary/Mythical Pokemon in all of Pokemon Go, yet it doesn't really get the respect it deserves in GO Battle League.
Its maximum CP of 3,791 means it is almost by default considered a good pick for Master League but the general consensus is that the Iron Leg Pokemon can be looked over for Ultra League. We think that's a little shortsighted and here's why.
Metagross is a dual psychic and steel-type. This means it matches up well with a lot of species.
It is only weak to dark, fire, ghost and ground-type attacks. Metagross' resistances far outweigh its weaknesses, though. It has resistance to dragon, fairy, flying, grass, ice, normal, rock and fellow steel-types. In addition to this long list it also has double resistance to poison and psychic attacks.
This means that in your an average match up Metagross is coming out on top. Be careful of the likes of Excadrill and Heatran who will decimate the pseudo-legend.
A needed counter to fairy-types
Anyone who has played a lot of GO Battle League will know that fairy-type Pokemon are popular picks. They are the perfect counter to the infuriatingly strong Giratina and other various other frequently used dragon-types.
They are seen so often that you need a plan in place to counter their counter. At the top of the list is Togekiss, the fairy-type that can reach the highest CP. That isn't the only one you'll come across, though. Clefable, Gardevoir and even Alolan Ninetales will all invariably defeat the likes of Giratina and the other various dragon legends such as Dragonite, Palkia and Rayquaza.
Fortunately, Metagross will handle all of these with ease. So, so far we have a Pokemon that is not only resistant to a lot of types but is the resolution to all those pesky fairy-types, too.
Metagross' moves are arguably its most appealing asset. There's little question that Bullet Punch is the best steel-type Fast Move.
It generates 3 damage per turn and 3.5 energy per turn. This makes it the best energy generating move among steel-types and second, only behind Steel Wing, for damage.
It's a move that many Pokemon aren't capable of learning either. In fact, the only other steel-type Pokemon capable of it is Lucario, but many players prefer to use Counter as its Fast Move.
Metagross also has some devastating Charge Moves it can learn. The best of them is the Elite Charge Move Meteor Mash. It is a steel-type move that hits for 100 damage while only requiring 50 energy.
Of course, Elite Charge moves are hard to come by and will cost you a precious Elite Charged TM. Earthquake, Flash Cannon and Psychic are Metagross' alternative options. Of those Psychic requires the least energy at 55 which probably makes it the best bet considering the importance of being able to quickly use Charge Moves in Pokemon Go's GO Battle League.
Earthquake and Flash Cannon shouldn't be disregarded though, as they provide 120 and 110 damage respectively, both for 65 energy. Having two Charged Attacks here is ideal but will set you back a massive 75,000 Stardust. Besides if you're going to have two Charge Moves then you may as well make one of them Meteor Mash if possible.
There you have it, we've seen other analyses that somewhat demeans Metagross' potential. Due to the above, we can't see why anyone wouldn't consider the steel-type 'mon - as it has everything you could want from a Pokemon!