Imo, Emboar doesn't make a very good wall, 4 weaknesses and low defences with a moderate-high HP.
Instead, I would give it a sweeper set:
Stone Edge/ Earthquake
Hidden Power (electric/ water)
Gengar: I would switch to a Sp. Attacker, since it's attack stat is really low. Something like this:
Focus Blast (coverage)
You can make it hold Black Sludge as well.
Flygon's x4 Ice weakness is really crippling, so you either need to know what your opponent is going to send out, or it's going to get KO'ed w/ Ice Punch or Blizzard before you can even use it.
I would suggest another Dragon type? Or maybe an Electric type for coverage. Nothing wrong with Flygon, but in competitive play, there are better choices. Garchomp, with the same typing, is a better sweeper, having higher speed & attack stats. Imo, you could replace Emboar with Garchomp, but I'd understand if you wanted to keep your starter.
@ Expert Belt/ Leftovers
Stone Edge (type coverage + Ice weakness)
Dragon Pulse (STAB)
Crunch (type coverage)
If you want an electric option, Rotom-Wash is a good one. Also, Rotom-Fan or Emolga have an interesting Electric/ Flying typing. Despite Emolga being frail and Rotom-Fan having a limited move pool, they're pretty fun to use. If you want on for OU, go for Rotom-Wash.
Item: Water Gem/ Cell Battery
Item: Light Clay
Role: Defence support
Thunderbolt/ Air Slash
With Metagross, there's no point trying to raise speed that isn't really there, because by the time you do so, Metagross could have taken a lot of damage already, so I would go for Stealth Rock or Toxic instead of Agility. I would also replace Hyper Beam with Hammer Arm. You need to recharge with Hyper Beam, and Metagross shouldn't care about speed anyway.
Toxic/ Stealth Rock
Another option could be Skarmory, since it can set up both Spikes & Stealth Rock.
I would recommend Mienshao instead of Hitmonlee, with this set:
Item: Expert Belt
High-Jump Kick/ Aura Sphere (depends if you're feeling lucky or want some mixed damage)
Stone Edge (type coverage)
Regenerator U-Turn Mienshao is a good combo, since it will regain 33% of its HP upon switching out, along with Drain Punch being damage & heal at the same time. Stone Edge for flying types, and U-Turn to escape from Psychic types while dealing x2 damage.
Walrein has a horrible typing (Ice negating almost all the resistances water has), so instead I would recommend a healer/ support instead, such as:
Ab: Serene Grace
Drain Punch/ Flamethrower
Drain Punch/ Shadow Ball is there to prevent Togekiss from being trapped by Taunt. Either Drain Punch for heal stall, or Flamethrower for type coverage (since Drain Punch is x0 against Ghosts), and Serene Grace doubles the chance of burning.
Imo, Togekiss is one of the best heal supports, since it can learn both Heal Bell, Wish, in addition to a quick switch move, i.e. Baton Pass, coupled with a good sp. defence.