I like Pokemon so an army of that I could split into 6 branches: The Swarm, The Horde, The Legion, The Armada, The Haunting, and finally, The Pantheon.
They are separated by power level, then by role; the former has countless weak pokemon, the latter has heavy hitters. Psychic and Ghost pokemon would be perfect Special Forces!
Sea Pokemon could fill half the Armada, gangs tentacruels leading many tentacools and Gyrados Generals will battle your ocean forces, with the aid of Blastoise and Golduck before amphibious forces land and aid Air pokemon.
Or perhaps jusst an endless army of Dittos is more than enough. Hell, Eevee and all its evolutions will be sufficient to defend against any attack, but not always to go on the offensive, being a land based army. Just shoot down flying pokemon with any projectile or energy.
Maybe digimon or yugioh is more your style. I might prefer such units for my militaries, depending on how Wing Dragon of Ra or The Forbidden One compares to MewTwo, Kyogre, Groudon, and Ho-Oh!
Then again, ZOMBIES!
Resident Evil, House of the Dead, Land of the Dead, I Am Legend, and countless others of animated corpses with sub-human intelligence full of violence.
Or aliens and robots!
Or alien robot zombies. Necrons.
Hell, an Army of Gods is
...everything? You get points for working more from less!
As the evilest being in the universe, I chose an army of lolis and shotas
I will be unstoppable hahahahaha
those all stupid aliens demons and gods attack humanity with armies of monsters just to be wiped out by some hero or humans themselves.
But if I send an army of most cute lolis nobody will dare to hurt them all armies will give up and surrender all superheroes will be disabled by their cuteness
There will be no force capable to stop me.
And then like truly evil overlord I will send my army to rape men and women and even their children because, as we know, rape is the worst thing one can do.
Dragons. Fucking. Dragons.
If a single dragon could be capable of besieging an entire city, then an army of gigantic, armored, flying, fire-breathing monstrosities could take over entire nations at once.
No army could stop my conquest.