After I saw that one of the most wanted mega-pokemon was made in this game, I wanted to see what M-Flygon was able of.
First, we have to see the normal one. Flygon is Dragon/Ground type with the ability levitate. That means that when he comes on the battlefield, the only entry hazard that he fear is “stealth rocks” (6,25% of his HPs). But Flygon is defensively weak so it’s probably better to use him when one of your pokemon is K.O.
The M-Flygon now. Type dragon/bug. 80HP/110Attack/80Def/140Sp.Attack/80Sp.Def/130Speed. Ability: Amplifier (make sound attacks 50%more powerfull)
Well, at least we can say that his destiny is clear. He’s a sweeper.
I will propose to you 2 sets.
Set 1. DO I NEED TO REPEAT?!
Timid - 252 speed and 252 Spé.attack and 6 HP
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Ancient Roar (ROCK’n’roll baby)
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Bug Buzz (Bug… what?)
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Earth Power (Ground for those who live in Metchi town…tsss peasants)
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Drakon Voice (dragon)/ Boomburst (normal)
With a BS Speed of 130, you’re as quick as volteon and aerodactil…And you can break their soul with the less powerfull of your moves. Bug Buzz is your main stab. With the stab and his ability, Bug Buzz hit with a power of 202,5. Not bad I must say. Ancient Roar hit with a power of 120 and earth power with a power of 90. They are both here for the coverage. The last move is your choice. Drakon voice hit at 236,25 wich is incredibly huge. But it has just 85% accuracy. Boomburst have 100% but hit with JUST a small 210 (ability fuck yeah!!!). It’s your choice but you have to see that if you choose the first, you need an answer for the fairy-type and if you choose the second, you have to find something else for the ghost-type. It’s probably the best set of M-Flygon but our friend is weak to priorities and entry hazard once he had mega evolved. My advice is to use him like a revenge killer or a finisher and have a defogger in the team. Oh…and do I already said that all his moves are sound moves? (well…not earth power but it’s for the steel pokemons) That means that all the substitute users can already fled.
Set 2. DO I LOOK LIKE A FUCKING SINGER BRO ?!
Jolly - 252 Speed 252 Attack 6 HP
-Hone Claws (boost attack and accuracy)
-Earthquake (classic)
-Rock Slide (We have to do with what we got)
-Dragon Rush
Your opponent will clearly see in M-Flygon a brutal special attacker. And that’s why this set is good. Your opponent will switch on a special defenser and… forget that M-Flygon have 110 in ATK BS… U mad bro? 
With one Hone Claws, you can reach 479 in attack stat. And thank to the accuracy boost, Rock Slide and Dragon Rush will probably not miss. It’s clearly a gimmick set but it can work…probably (not tested for the moment )
Like the special one, he will thanks a defogger and don’t like priorities moves.
I hope you like it and I really hope that my bad english wasn’t too difficult to understand. If you have suggestions on others sets, don’t be hesitating! So leave a like, I want Torren’s youtube money! (I know where’s the door)
But yeah, it’s not really like he was weak against them before becoming the mega.