(Please keep in mind that I'll mostly be answering this for OR/AS, but this applies to US/M as well.)
Mega Camerupt has a lot of things going awry for it, which carry some major issues. These prevent it from being a bigger threat in higher tiers, but it's fine where it is. A few points of trouble for Camerupt are:
- Shallow movepool
- Bad base speed
- Extreme predictability
- Weak to two very common types in competitive
- Easily worn down
Despite getting a great buff to both its offensive and defensive stats through its Mega evolution, Camerupt struggles to make a significant impact in most higher tiers. That's not to say it's bad, however, as it still holds a niche as a powerful special attacker that can take on the likes of Mew, Mega Gardevoir, and any Electric-type not named Rotom-W. Additionally, Camerupt has access to Sheer Force, which boosts its two main STAB moves, as well as coverage like Rock Slide, Ancient Power, and Flash Cannon. It even has access to Will-O-Wisp, which is a great move to use on Pokémon like Azumarill on the switch. However, a 4x weakness to Water and a very low Speed stat stops it from being a top-tier threat. (It only outspeeds Ferroseed in RU.)
Camerupt is best used as a bulky special attacker to take full advantage of Sheer Force, which boosts the power of its STAB moves. Ancient Power, a niche coverage option, receives a boost as well, and it's useful for hitting the likes of Talonflame, Mega Charizard Y, and other Flying-types. The final slot is for coverage against Water-types with Hidden Power Grass or to cripple opposing physical attackers with Will-O-Wisp. Neither option is definitively better than the other, as it depends on the team. Hidden Power Ice can also be used to hit Dragons on the switch, as it OHKOes Garchomp and does upwards of 50% to the likes of Latios and Latias. Needless to say, Fire Blast from Mega Camerupt, factoring in STAB and Sheer Force, will effectively have a massive 214.5 Base Power and will roast anything that does not resist it, and its STAB Earth Power also gets the Sheer Force boost.
Its good stats and ability are held back by its extremely shallow movepool and the easily predictable move choices that go with it. This is the worst Mega that was ever introduced and that includes Mega Audino. It has a base 145 Special Attack and Sheer Force to back up its moves when in reality, that's just as strong as Life Orb Chandelure (which is far from unmanageable), and a hell of a lot slower. Slowking also outspeeds Mega Camerupt, which is hilarious. It was one of the only two Megas allowed in NU at the beginning of the OR/AS and US/M phase. (Camerupt and Audino were the only NU Megas, Audino is still in NU. That's a plus for Camerupt as it was "good enough" to get banned from NU.)
If you're playing RU, please use any other Mega than Camerupt. Even if you're using the RestTalk set in US/M or OR/AS, you'll rarely find opportunities to crack it in any battle.
For more on Camerupt, check this out. It's an old analysis thread for Camerupt; its criticism starts from page 3.
