Okay so I saw sugarhigh nomming this earlier in the XY thread, and it seemed like he was ignored, so I'd like to bring it back up again.
I think Mega Houndoom should be moved up to B rank. At first, I didn't really see any reason to run Mega Doom. It's fairly weak because it can't hold a boosting item, and its STAB moves are resisted by common Pokemon such as Greninja, Azumarill, and Tyranitar. On top of that, its got a pretty useless ability unless you're balzy enough to use it on a sun team or something. However, I started testing it a few days ago because I thought it had some potential I just wasn't seeing. Lone behold, I was surprised to see how it excelled quite well in most of my battles and how a lot of offensive teams can have trouble dealing with it. Its typing is actually really cool defensively and offensively, as it is able to stop Mew cold, one of the best support Pokemon in OU, and use it as set up fodder, as well as Mega Sableye, who can't really touch Mega Doom at all. On top of that, its ability Flash Fire, before Mega evolving is really useful, as it can set up on defensive Heatran with Taunt.
And that's the cool thing about Mega Doom. It has a few cool options which makes its last moveslot rather unpredictable and easy to tweak depending on your team. For example, the team I'm using in particular struggles a bit against defensive cores that carry Heatran. So to fix this, I used Taunt in the last moveslot so I can use it to grab a free NP boost and potentially sweep. Taunt is also useful against Chansey, because if you manage to pressure Chansey enough so that it becomes weakened, you might be able to actually bust through Chansey with Mega Doom, because once its Taunted it's forced to Seismic Toss you, so you can just continually do this until it's worn down to a point later in the match where you can set up on it and beat it. Taunt is also useful for preventing shit like CM Clefable and Mega Sableye from setting up on you, while you can return the favor. It also has other cool useful moves at its disposal, particularly Will-O-Wisp which lets you burn shit on the switch, such as Azumarill, Tyranitar, Dragonite, Mega Diancie, Mega Altaria, Mega Gyarados. Both moves are equally viable, and are all dependent on what your team needs and what your weaknesses are. If you find yourself struggling against defensive cores, then Taunt is preferred. However, Wisp lets you lure in its common switch-ins so that they're heavily crippled and you can potentially use them as set up fodder later on in the match for something else. There's other cool options such as Destiny Bond, which lets you suicide on Pokemon that you can't OHKO and eliminate them for the rest of the match, which can prove to be very useful.
All in all, Mega Doom is a heavily underrated Mega evolution that is greatly undermined for its lack of amazing coverage as well as a pretty mediocre ability, however it checks a lot of top tier threats in the current meta, such as the Lati twins, Slowbro, Ferrothorn, Mew, Heatran, Mega Venu, Mega Scizor, Gengar, Mega Metagross, and Mega Sableye. It can also disrupt a few common defensive Pokemon that give offensive teams trouble, and despite its somewhat subpar SpA stat, it can actually sweep quite frequently when given the right support. I just think Mega Doom fits a lot better with the B ranked Pokemon than many of the VERY niche Pokemon found in B- rank. It's better than most of them.
Also please refrain from commenting on Mega Doom if you've never used it before. Many of the arguments I see against it in the other thread clearly had no clue what specific niches and uses Mega Doom has, and simply stated all the common checks and counters it had while ignoring everything else.
