1. How does the card stand on its own? Is it good, bad, or has potential? Is it worth playing?
Donphan really can be a beast on its own. He is basically a tank. He can hit hard and take hits very nicely. The Poke-body is what makes him a tank. The ability to reduce 20 damage for every hit it takes is very nice. His ability to hit for 60 for one energy is really why he is very popular. Through this attack, he can donk. Now that's monstrous. Of course, I'm not so sure if you'll be using Earthquake (90 for 3 {F}) though as it really does cost lots of energies. Thus, it is good, has potential, and it is worth playing, especially when it comes to countering Luxray Gl Lv.X
2. What popular metagame decks is it used in?
There are lots of decks Donphan is used in, but I'll name a few that are actually quite recognizable. Flyphan is one deck. It uses Flygon and Donphan as main attackers; however, the deck also uses Flygon to give Donphan a free retreat, which greatly helps because Donphan has a heavy retreat cost. Another deck that, right now, is the most focused on Donphan deck is Donphan/Uxie. This focuses heavily on Donphan, with Uxie used for drawpower. It will also run 1 Relincanth too. The deck will notably use lots of trainers as well.
Now that we talked about the decks we see Donphan as an attacker, lets talk about the decks that seems to use Donphan as a tech. That's right, Donphan has been used in decks as a tech. The main reason? To counter Luxray GL Lv.X. One deck that seems to use this is Gyarados/Luxray. It is your average Gyarados, but it has Donphan as a backup for attacking Luxrays that come in your way. Of course, there my be other decks using this concept too, but I'm not so sure of which other decks will use Donphan as a tech since Gyarados is the only one that comes into mind.
3. What comboes can you use it with? How so?
Manectric really does come into mind. Have one in play on your bench, and then put a Bench Shield on it, and Earthquake won't be making any damage at all to your bench. Nidoqueen seems to come into mind as well. It lets you heal Donphan every turn. Out of the two though, Manectric seems to be better because it is a stage 1; so, it is faster to set up. Nidoqueen would work when you run Donphan with a stage 2, like Flygon.
4. Give it a rating and exxplain why you would give it that rating.
I would give Donphan a 4/5. Donphan is a really good card. He has a very nice potential to donk with an attack that can do 60 for one {F} energy. He can even take damage very nicely because of the Poke-body. Since he is fighting and has {L} resistance, he is an excellent counter to Luxray GL Lv.X. Now the main problem with Donphan is that he has {W} weakness, which really hurts because of Gyarados and Kingdra being in the format right now, and it has a very heavy retreat cost, so you may need to consider runnning Warp Energies, Switches, Warp Poins, Super Scoop Ups, or maybe even Flygon.
5. How's the artwork?
It does look cool I must say. Donphan really does look like its giving you an evil stare. It even gives you the look that says, "I'm ready to battle!" The shine of his tusk really emphasizes this also.