Ahh, I remember the random matchup days! I think I'll rate.
Flygon: He looks good, but Outrage and Dragon Claw are useless, so give him Fire Punch to take care of Scizor. I like the U-Turn set on this guy to take care of lead starmies.
Magnezone: I don't know if charge beam is worth it. It's not that powerful, so you might as well go with thunder/thunderbolt. As far as I know, random matchup battles don't last TOO long, so he won't have that much time to raise his stats.
Scizor: Umm, well, do you remember our battle? My Scizor CLEARLY beat yours. It needs bulk, and scizor does great tanking with bulk. SO!
Scizor @Life Orb
Trait: Technician
EVs: 252 HP/ 252 Atk/ 4 Spe
Nature: Adamant (+Atk, -SpA)
-Bullet Punch
-Bug Bite
-Superpower
-Swords Dance
You can usually sweep teams with one or two sword dances. Then you bullet punch. This scizor will work well-- Trust me, I've done random matchup before. He can survive superpowers, earthquakes, close combats and some other stuff.
Rotom-W: You already have an electric type. You can choose between this guy and magnezone, but one of them probably needs to change. Mold-Breaker Haxorus can hurt both of your electric pokes, easily popping Magneton's with a brick break, then finishing the job he started with an EQ. SO! How about something else.... I have a good Idea. This guy does REALLY good in short battles-- He just tears a hole in the opponents team... I present to you...
CONKELDURR!!! @ Toxic Orb
Trait: Guts
EVs: 252 HP/ 252 Atk/ 4 SpD
Nature: Adamant (+Atk, -SpA)
-Drain Punch
-Mach Punch
-Stone Edge
-Bulk Up
Random matchup battles are usually not that long, and Conkeldurr with toxic orb is as powerful as he would be with a choice band! With one bulk up, you can mach punch and really just destroy the opponent, or drain punch to regain some HP. Toxic orb is the way to go in short battles, and Stone edge covers flying.
I've done random matchup, and this will definitely help your team. Good Luck!