Look, I really like Mega Camerupt, but I also think it's being overplayed a lot in this thread. I get that this thing hits like a semi, but you need a lot more than raw power to really succeed in OU. One cool perk about Mega Camerupt's bulk and defensive typing is that it lets Camerupt check the Electrics, which is cool, but besides that and obvious stuff like defensive Grass-types, it doesn't switch easily into much else. It has a great Fire resistance, but it can't safely switch into Charizard Y for fear of a 2HKO from Fire Blast (almost guaranteed with Modest or Timid + SR), Heatran for fear of Earth Power, or Talonflame for how hard Brave Bird hits. Fairy resistance is great, but Mega Gardevoir's Psyshock 2HKOs after Stealth Rock while Fire Blast can't OHKO back, Calm Mind Clefable just uses you as setup bait, and Azumarill obviously obliterates Camerupt. It also has no form of recovery, which hinders its ability to take hits over longer periods of time, and it's bulk isn't even that amazing. It's only about as bulky as Keldeo on the special side and slightly less bulky on the physical side, which is good but not amazing.
The really low base speed is a very legitimate problem as well. Solid bulk will only take you so far when you're pretty much forced to always take a hit before actually being able to retaliate. While something like Landorus or Greninja may not be able to take a hit nearly as well as Mega Camerupt, it still has a better shot at actually surviving longer if it can outspeed and KO opponents before they have a chance to hit it rather than having to tank hits before even getting the chance to move. I get that such a low speed stat can be good for Trick Room, but if Trick Room was relevant enough to make a Pokemon really viable, then Mega Abomasnow would at least be ranked in the viability ranking thread, lol.
The other big thing I think that really hurts Mega Camerupt is simply the fact that it's a Mega Pokemon. Face it, with all the new Mega forms that arrived in ORAS, the competition for a Mega slot is tougher than ever. While Mega Camerupt can switch into Electrics really well and hit super hard, there are other Mega Pokemon that can do one or both of those things as well while also offering other substantial perks of their own. For example, Mega Charizard X can also check Electrics decently enough while having an even more powerful nuke in Flare Blitz, better neutral coverage between its STABs, better physical bulk, real speed, and reliable recovery to make up for the lower special bulk and to give it significantly greater longevity. It can also take on things like Bisharp, defensive Mew, and Mega Scizor more effectively thanks to the aforementioned greater physical bulk and speed, not to mention that its double Fire resistance makes it better against Charizard Y.
In its own right, Mega Camerupt is a pretty cool Pokemon, but there's just not a ton of incentive for me to use it over other Mega Pokemon unless I just really wanted to use Mega Camerupt. Hitting really hard and checking Electrics is great and all, but when I can do the same thing with Mega Charizard X or do similar things with other Mega forms along with a number of other advantages, I'm probably going to go with them.