Camerupt is an oft overlooked Pokémon, capable of stopping some of both the UU metagame's biggest threats. The RestTalk set is probably the most effective set to use in UU, where status runs wild and very few Pokémon can safely switch in. The Choice Band set's effectiveness is dependent almost solely on prediction. The tank set's strength lies in supporting the team. The Pokemon that Camerupt draws in are fantastic, ones that usually are crucial in walling other dangerous Pokemon, and if you use Camerupt to get rid of them you can go for a sweep.
Camerupt, with its unique Fire / Ground Typing, walls Electric-Types quite effectively. With the massive EV investment in SpD, even a Zapdos with 383 SpA (the highest of any Electric-Type) only manages to do 24% - 28% with Hidden Power Ice or Grass. Timid Raikou's unboosted Crunch only hits for 23% - 25%, making Camerupt one of the best Calm Mind Raikou counters in the game. Though by far the most effective of its uses, Camerupt's walling potential is not limited to Electric-types. It switches in on Weezing with relative ease, though Sludge Bomb does take its toll. Heal Bell Celebi's Psychic only does 28% - 31%, while Fire Blast hits for 67% - 79%. While Camerupt doesn't exactly wall them, it can be used to beat Jirachi, Jynx, and Alakazam in a pinch. Wish Jirachi has only about a 1% chance of 2HKOing Camerupt with a +1 Psychic, while Camerupt has an 80.7% chance of 2HKOing Jirachi with Earthquake. Jynx and Alakazam miss out on the 2HKO and are both OHKOed by Earthquake.
In UU, Camerupt stops, but falls short of beating, the ever popular Hypno + Vileplume combo. Sunny Day + Solar Beam users, barring nasty luck, are shut down, and Victreebel can be walled in a pinch. Ninetales, Manectric, and Electabuzz have no chance of overcoming Camerupt without Hidden Power Water.
Rest and Sleep Talk, combined with a sandstorm immunity, gives Camerupt some much needed durability and allows it to completely wall special versions of Gengar. Letting it utilize dual STAB is an obvious choice, with Ground and Fire only being resisted by Flygon, Salamence, Gyarados, Moltres, and Charizard in OU and Mantine, Solrock, and Lunatone in UU. If being used in UU, Fire Blast completely outclasses Flamethrower. However, in OU, you may find your Fire Blast PP getting rapidly depleted by Zapdos, Suicune, and Dusclops, which makes Flamethrower a suitable replacement.
A set tailored to the OU environment, though it also works in UU. Many players will give all of one-turn for Camerupt before it either has to switch out or get killed, and Choice Band lets Camerupt make the most out of it. A boosted Earthquake will put major dents in bulky Water-types, while your Fire-move cripples the other half of physical walls. The third move is really just filler, allowing you to stop Gyarados and Salamence from walking all over you if you have good prediction. And even then you could just unleash an Explosion on them, and perhaps open up a sweep for a SubSD Heracross or the like.
This is basically a diluted, less prediction-based version of the Choice Band set. Power is sacrificed for ease of use and the ability to switch in. The first time Camerupt gets in, the first move it should be using is Toxic. It cripples its most common counters, Water-types, and with Fire Blast and Earthquake looming right overhead, opponents won't take the risk to switch in a Steel-type or something with Natural Cure. Afterwards, Toxic should be withheld unless their originally statused Pokemon can no longer switch in. Explosion gives you the opportunity to wreck another Pokemon on your opponent's team.
Eruption can be used just to flaunt how cool a Pokemon Camerupt is (conversely, it can also easily show how pathetic it is), but its other Fire-moves are more reliable.
For the Sleep Talk set, HP is foregone for Special Defense because the only physical attack Camerupt should be taking is Sludge Bomb from Weezing / Vileplume. Attack investment is needed for some important OHKOs and 2HKOs, as well as giving bulky Water-type switch-ins a nice parting gift.
Choice Band Camerupt needs all the firepower it can muster, while the tank set requires a mix of bulk and power.
Checks and Counters
Lunatone and Mantine take Camerupt's STAB like a champ, though a Choice Banded Rock Slide still hurts. Bulky Water-types work, especially since they almost always carry Rest and don't fear Toxic. Hidden Power Water Electric-Types will completely turn the tables on Camerupt as well.