My troops would consist of a variety of Pokemon:
Diglett: Chosen over Dugtrio for its more compact size. A squad of these could collapse the ground enough before a battle to create an advantage, or after to quickly end it if I am losing. Diglett can also be used to attack infrastructure or create underground tunnels for escape or sneaking about.
Koffing / Kecleon: As part of an infiltration squad, Koffing and Kecleon will act together. First, Kecleon sneaks into the enemy base and then Koffing smokes them out. Kecleon is then able to do whatever it needs.
Porygon: Porygonz in yo compootz, mesin up yo hard-drive.
Scizor: As a fast and well-armored warrior, Scizor can act as an infantry shocktrooper. It can defeat foes quickly with its immense power and pick off the ones which are barely surviving.
Metagross: Another Steel-type for their resilience. Metagross would act as a heavy tank sort of unit. It would use its Hyper Beam to attack at a long range. Those who come within its minimum range would get a face full of Psychic. A group of them would be capable of incapacitating enemies and could even stop incoming projectiles with Psychic. If needed, Metagross could attack from the air with Magnet Rise.
Bronzong: Bronzong takes a role similar to Metagross. It will serve as light artillery by using Flash Cannon. If necessary, it can plow through the enemy using Gyro Ball. Other roles would be to mess up the weather and set up Stealth Rock so the enemy infantry is picked off before it reaches Metagross.
Abra: Abra is known for having one of the strongest telekinetic shields in the world! It would escort high-tanking commanders and protect them if necessary with Safeguard. Teleport is also an option for increased mobility and escape. Small size over its evolved forms for convenience.
Altaria: My sole air attacker, barring Metagross, since he can't stay up in the air forever. Instead of doing the bombing thing like normal air troops, Altaria enters low altitude with a Safeguard up to prevent AA from defeating it. Then, it uses Perish Song and escapes if possible. Altaria can take on other air units like a fighter using Flamethrower and Dragon Claw.
Overall, Psychic forces are pretty overpowered. Attacking from the air? No problem. Bend the air waves so the attack is fired back at the enemy. Attacking from the water? No problem. Lift the enemy out of the water and blast them away. Hell, we could probably even create a temporary trench to impede water movement with enough psychic powers.
My strategy? Incapacitate the enemy: cut off their communications with the outside and destroy their infrastructure. Prevent mobility of enemy by taking advantage of environment and weather -- stop the advance of more troops. Then, pick off every last enemy within the closed battlefield. Defend using telekinetic shields.
Oh and:
Smeargle: The all-purpose trooper!
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Also, my alternate squad... Since you can't beat the dead, ever:
Gastly: And a lot of them. They are impervious to all types of physical attacks and can put enemies to sleep at his will. Gastly can suffocate the enemy by engulfing them in its gaseous body.