I agree about all this "prediction" stuff, Lee. Any pokemon can be countered if you switch in properly. If you come in on the right move, you can get an advantage... people saying stuff like Primape and Omastar are unbeatable probably made a bad switch and got their counter killed.
You can switch lots of things into Primape. Ghosts wall almost it's entire set, Toxicroak walls it... theres plenty of things that can come into one ore more of it's moves. Just like it takes prediction to use a choice bander, it also requires prediction to counter one. Thats why Pokemon is such a great game... it always keeps you on your toes. (even though the graphics and sounds aren't exactly riveting)
Now about Omastar. Being such a crappy type, it's going to have a hard time switching in. Most water types wall it almost entirely, taking hits only from Ancient Power or Hidden Power. It hits really hard, but unless it's running timid, tons of stuff outrun it, even in the rain. Any bulky grasser can come in on most moves and OHKO it, and considering how many there is in UU (vileplume, bellossom, meganium come to mind) it's not unstoppable.
Omastar also has the four moveslot syndrome. With one move being taken up by Rain Dance (if it sets it up alone) and another by Surf, you have to choose between HP Grass, HP Electric, Ice Beam and Ancient Power. If the opponent knows your moves, it's easier to counter. If it doesn't set up rain dance by itself, then you have to predict when it'll show up, and hit it with a SE move, or sub, or stat-up.
@ Cynthia, I agree that Shuckle is good, but Swellow, Kingler, Crawdaunt, and other hard hitters still 2HKO it. The aforementioned Omastar beats it as well. Vileplume can change the weather and solarbeam it to death. Just switch in Swellow on SR, and switch the crabs in on Encore, and switch Vileplume into Toxic.
Heres some calcs folks, its not hard to take down. I'll only mention the pokemon I just listed.
-Adamant 252 Swellow's Brave Bird on 252/252 Impish Shuckle:
38.93% - 45.90%
LOL, ok, that doesnt work... 3HKO, 2HKO with SR up.
-Adamant 252 CB Crabhammer Kingler on 252/252 Impish Shuckle
78.28% - 91.80%
HA HA HA HA p4wned. OHKO in the rain or with SR up.
-Adamant 252 CB Crabhammer Crawdaunt on 252/252 Impish Shuckle
73.77% - 86.89%
Nearly as much as Kingler. Next!!
-Modest 252 Omastar Hydropump on 252/252 Careful Shuckle
63.93% - 75.41%
Hmmm, less than I expected, but in the rain in could do some damage. Possible OHKO with SR or Rain.
Modest 252 Vileplume's Solarbeam on 252/252 Careful Shuckle
29.10% - 34.43%
Not a good counter.
Adamant CB Aggron iron Head on 252/252 Impish Shuckle
62.30% - 72.95%
Heh, just for fun, I decided to do Aggron. Turns out he 2HKOs it :D
PS: Hi shiney oddish. Somehow I passed you in posts : O