Covering the majority of these problem mons in one is a tall order, but I think this is a good idea:
Heatran @ Chople Berry
Ability: Flash Fire
Level: 50
EVs: 212 HP / 252 SpA / 44 SpD
Calm Nature
IVs: 0 Atk
- Fire Blast / Magma Storm
- Earth Power
- Ancient Power
- Toxic
This is a very clunky-looking set but it's specialized for the team. "FerroTran" is a decent core to begin with, the shared Fighting weakness not only covered easily by Salamence and Azumarill, but also mitigated by Heatran's Berry, while Ferrothorn and Salamence have Heatran's Ground weakness covered. The Chople Berry is honestly there only so it has a fighting chance against Thundurus variants of all stripes, allowing Heatran to stomach an LO Thunderbolt followed by a Focus Blast and still win 1v1. But you never know, it might be clutch in a situational emergency, too. The HP and SpD investment with a Calm nature give Heatran the most special bulk, avoiding the 2HKO from LO Thundurus Thunderbolt. Special Attack is maxed out because Heatran needs all the power it can handle if it's going to muscle past some of the threats that plague the team. If you're not really worried about having the extra SpA, you can run with the 212 HP / 4 Def / 44 SpA / 156 SpD / 92 Spe spread as mentioned on the analysis, as this set is still capable of 2HKOing Thundurus with such a spread. Toxic is in the last slot to let Heatran get rid of Cresselia/Porygon2 for the team much more easily.
This seems pretty good, but the biggest problem I notice is 252 SpA and a Calm nature. Tran's higher SpA means Modest with SpD EVs is better, or at least it should be.
I think Flamethrower and Lava Plume are also good ideas for attacks, but you'd run les SpA with the latter. Chople Berry seems kinda odd at first with the situational nature of type resist berries, especially when fighting isn't even Tran's biggest weakness. But I think it' justifiable with the team's current problems. I also agree with the other moves, I was doubting Ancientpower at first, but I thot about it and realized it's probably more reliable vs Thund, and gets Char Y and stuff.
Tran deals with quite a few threats to the team, but makes some problems too.
Suicune was kind of a pain anyways, and now it's really bad I think. Nothing really wins against it except Ferro if it somehow never gets burned, highly booted Mence, or Azu with crit.
Garchomp is bad, and I don't think it's just limited to SD. Ferro depletes itself on Rough Skin while not doing TOO much, and fearing possible fire moves. Mence needs boosts and maybe status to win which isn't really likely. Azu has PR but that can miss, and it'll take at least one Rough Skin best case scenario. It's also chunked heavily even by non CB or boosted Chomp, so if it's already low health...And Heatran just dies to all Chomp in any scenario that's feasible.
Kangaskhan I don't really like the match up. Kinda rushed o can't get all the data maybe, but I know Ice Punch/Beam and Fire Punch/Blast aren' unheard of. Those get rid of Mence and Ferro, though Mence also dies fine to Rock Slde, especialy in conjunction with Secret Power. Azu really can't win often at all, and never vs full health Kang. Tran can do ok vs. non EQ, but that can be a lot too hope for, and RS shenanigans still do good. Really Kang is same kinda deal as Greninja where probably no on beats everything but it has los of options and will often get you.
Slowbro is really unbeatable, not even any chance of crit hax on the mega.
Rotom-Heat @ Sitrus Berry
Ability: Levitate
EVs: 252 HP / 252 SpD / 4 Spe
Modest Nature
- Volt Switch
- Overheat
- Will-O-Wisp
- Thunderbolt
I'll nominate
Rotom-Heat again. It's still good for the reasons I mentioned before (we still need a solid Thundurus solution), and is possibly even a better fit now that we've added the Talonflame-hating Ferrothorn.
Since the Ferrothorn build we've chosen both acts as a Spore absorber and has Leftovers, I'm recommending the conventional tank build from the dex entry.
Gengar @ Gengarite
Ability: Levitate
EVs: 188 HP / 116 Def / 4 SpA / 4 SpD / 196 Spe
Timid Nature
- Destiny Bond
- Hypnosis
- Hex
- Focus Blast
Now that we have a full core selected, it's worth considering a backup mega.
Casino Gengar has been my go-to for that role recently. In addition to the "delete target Pokemon with Destiny Bond" utility that comes built-in with Mega Gengar, this build has the ability to, with some luck, cripple and remove multiple members of the opponent's team.
Hypnosis is great in general with this fast and bulky build, but it's especially effective when trying to avoid Sucker Punch mind games and on predicted switches the turn that Gengar mega-evolves.
Focus Blast is primarily for the Tyranitars that stall teams almost always bring against Gengar, but it's also useful against Kangaskhan, Porygon2, Ferrothorn, and more. (Missing doesn't hurt as much when they're asleep!)
No matter how well you craft your team, sometimes your opponent has one or more mons that you can't deal with effectively or their team just generally matches up well against yours. In these cases, coin flipping your way to victory can provide a better chance of winning than anything else you can do. Casino Gengar provides that option.
I still like Rotom-h on this team, but I don't get a Modest nature with 252 SpD evs. A Calm nature with SpA evs would probably be better cuz Rotom forms have slightly higher base defenses than base SpA.
Casino Gengar is much the same for me, just being a realy good chance to ruin something and rarely ever being a bad pick. Why not 252 HP tho, since Gengar's base HP is pretty low and lower than its defenses.
While I think these two would be good to add, there's still big Suicune problems. Rotom-h can't really beat boosted Cunes or faster ones that CM before it attacks. Gengar can be ok, but if Chesto Berry is intact it'll heal off a Hypnosis, and non statused Hex doesn't do that much. Plus there's the possibility it already has cm boosts and won't take much damage at all. Greninja is still pretty bad, as are Chomp(scarf EQ on Gengar for instance,)
Still I like these two-both deal fairly well with Slowbro, which is good since that was previously unbeatable. Kang is a bit of a problem still, but Gengar can fish with Hypnosis against it and kill weakened ones with FB. Rotom-h kinda just loses tho, not living DE, and the ones without that will almost certainly have Rock Slide.