1. How does the card stand on its own? Is it good, bad, or has potential? Is it worth playing?
I think Flygon Lv.X is good on its own. Its Poke-body, Wind Erosion, can discard the top card of the opponent's deck between turns if Flygon Lv.X is your active Pokemon. Wind Erosion can be pretty annoying, especially when a useful card is thrown into the discard pile. Plus, it also has an attack that can be very annoying against decks that rely on Pokemon Lv.X. You can choose one of your opponent's Pokemon Lv.X, and you do 150 damage to that Pokemon! That' literally a OHKO on most Pokemon Lv.X. Indeed, it looks like Flygon is good on its own, and it can be worth playing, but just remember to watch out for Garchomp C since Flygon is weak to it.
2. What popular metagame decks is it used in?
There have been many decks that have used Flygon Lv.X. These decks include Flychamp, which uses Machamp and Flygon as attackers, and as of now, Flygon/Torterra, which uses Flygon and Torterra UL as attackers. Yet, I noticeable thing is that in most Flygon decks, Flygon Lv.X wasn't that much of a general focus, as the main deck that actually uses Flygon Lv.X as the main attacker is Stallgon (sometimes called Flytrap). Here, with the help of a Memory Berry, you use Trapinch SW's first attack to prevent the defending Pokemon from retreating. At the same time, using this method, you can potentially begin decking out the opponent, which eventually goes to the point they end up losing by being decked out. Yeah, Flygon Lv.X has been used in many decks over the years.
3. What combos can you use it with? How so?
To take advantage of the Lv.X, I would obviously use the Trapinch from Secret Wonders. As mentioned, I would use its first attack, with the help of Memory Berry, to prevent the defending from retreating, and at the same time, keep taking the top cards of an opponent's deck bit by bit to the point they eventually get themselves decked out. I would also try Chatot G or Slowking with Flygon Lv.X. Using Chatot G or Slowking, I can arrange the top cards of the opponent's deck in a way so that some of their most useful cards are thrown away into the discard. Certainly, looks like Flygon Lv.X can have some nice combos.
4. Give it a rating, and explain why you would give it that rating.
I would give Flygon Lv.X a 3/5. Flygon Lv.X is indeed a decent card. Its Poke-body can be pretty annoying. In fact, the Poke-body can be used in so many ways that can turn this card into a pretty annoying card. Its attack can also be pretty ferocious, especially since you can potentially OHKO most Pokemon Lv.X using it. The big downside with this card, sadly, is the weakness to Garchomp C, and since Garchomp C happens to be very popular in our format right now, Flygon Lv.X can't take as much fame as it used too. Still, Flygon Lv.X still continues to be a nice card to this day.
5. How's the artwork?
I definitely have to say, that looks like a pretty epic artwork for a Flygon. Flygon looks pretty fearsome here, especially since it literally looks like its going to fly off the card and into the battle scene.