I go back and forth on whether this or Thundurus is the star of the plasma deck. While Thundurus lets you get away with using only special energy, Deoxys increases damage output, something that is just as broken (if not more). The best part about Deoxys is how easy it out. With search cards like plasma ball, it should be no problem getting 2, 3, or even all four of these out. Thundurus can do up to 70 damage for one energy, Kyurem can do the same plus 30 to the bench for 2. And one snipe from Kyurem can set up a 3 prize EX KO with Lugia. Best of all, the boost stays as long as Deoxys is on the field, so the more turns you have him out the more extra damage you're going to do. I don't think I need to explain why that is good.
The attack is pretty good too. It's situational since it a) needs a plasma energy and b) depends on how much energy is on the defending pokemon, but it can be a great counter attack when the situation calls for it. It even beats Mewtwo EX (assuming both have two energy attached and you're not playing PTCGO) while Mewtwo would be 10 short (180 vs 160).
10/10 for the plasma deck. It's that good.