Awesome Pokemon that suck

Serious response:

You decide. If you use the Pokemon and it gets knocked out before you can really enjoy having it out, it's up to you to decide of it sucks or not. Xatu was never really useful to me, but it's a pretty cool Pokemon. In Gen IV it does have Heat wave + Psychic + Signal beam to work with, but that's pretty much one of the best offensive movesets it can really have. It's very limited in its use, and will usually go down in one or two turns. Luckily it has pretty nice speed, otherwise it'd get wrecked by anything of equal or greater level to it.

In the single player game I keep it around and occasionally send it out if I know it can beat whatever I'm sending it on. In an actual battle (doesn't have to be competitive battle, a tough in game battle is enough) then I'd save it for when I'm desperate, because it'd get taken out fast.

By that chart...

Flareon, Glaceon, Leafeon, Eevee, Rapidash, Absol, Tentacruel, Seviper, Cherrim, Venomoth, Beautifly, Sableye, Sharpedo, Ursaring, Nidoking and Blaziken i'd put forth, off the top of my head.