Hi there! This is a solid team, I love the Bronzong + Tentacruel core and you have most of the metagame's main threats covered. However there are a few issues to consider. First of all one glaring weakness stands out to me: Mega Sharpedo. It can easily sweep your team after a little bit of prior damage with a moveset of Crunch / Waterfall / Ice Fang since it resists both priority moves on your team. As CBU pointed out you also have trouble against Mega Swampert in rain. Finally although Jellicent is immune to Fighting, it is weak to Knock Off and Pursuit, meaning that it isn't as reliable defensively as you might like it to be. Therefore my first suggestion is to try out a
Rest + Sleep Talk Gyarados over Jellicent. Gyarados is a much more reliable counter to Fire and Fighting types like Mienshao, Entei and Heracross, but primarily it offers a very solid answer to Mega Sharpedo and Swampert. Factoring in Intimidate, Crunch does a paltry 35% max while Swampert's Ice Punch manages only 17%. Consequently roaring out Sharpedo erases its speed boost, allowing Virizion to check it easily. It also retains Jellicent's ability to phaze out setup sweepers like Suicune, and in tandem with Toxic Spikes + Stealth Rock Gyarados can rack up quite a lot of damage on the opponent's side. Although Gyarados doesn't shut down Suicune completely, I think with the other suggestions in this rate Suicune is unlikely to cause you much trouble. One thing Gyarados lacks that Jellicent provides is obviously the Water immunity, but Rest means that a Scald burn proves nothing more than a temporary annoyance. Although Jellicent's ability to break stall will be missed, overall I think the defensive utility Gyarados provides far outweighs that. Besides, Gyarados can still prove more than a nuisance to stall with its ability to absorb status and rack up hazard damage with Roar. Here is the set I had in mind:
Gyarados @ Leftovers
Ability: Intimidate
EVs: 248 HP / 252 Def / 8 SpD
Impish Nature
- Waterfall
- Roar
- Rest
- Sleep Talk
Now with Jellicent gone, it's crucial that you have extra insurance against Suicune. So I'd replace Sludge Bomb on Tentacruel with
Acid Spray. This erases Suicune's Special Defense boosts and makes it much easier to deal with. Acid Spray also gives you a solid way of checking CM Florges. I'd also recommend adjusting Tentacruel's EVs a bit to a spread of
240 HP / 244 Def / 24 Spe which gets the jump on Adamant Honchkrow and Gyarados.
I'd like to propose a few minor changes now that I think will improve your team's overall performance. First is to switch out Mamoswine's
Expert Belt for a Life Orb, which is a must to take advantage of Mamo's amazing wallbreaking power. Next is to go with
Knock Off over Superpower. You don't have it anywhere else on the team and Knock Off really helps with breaking down defensive teams and crippling walls like Suicune and Swampert. I also don't think Bronzong's current EV spread and moveset are ideal. I'd run
Heavy Slam over Gyro Ball for more consistent damage against the likes of Florges and Mega Abomasnow. Gyro Ball fails to 2HKO Florges and also faces severe PP issues which can be crucial against Pressure users like Kyurem. I'd also recommend using an EV spread of
252 HP / 168 Def / 88 SpD with a Careful nature that offers a better balance of physical and special defense, allowing it to take on threats like Mega Aero, Shaymin and Nidoqueen equally comfortably. I'm honestly not a fan of HP Electric since its only target is Gyarados and apart from that it's useless. With physically defensive Roar Gyarados and Acid Spray you now have solid checks to it so I don't really feel it's needed anymore. I'd highly recommend going with
Toxic or Heal Block instead, which provide a lot more utility. The former still beats Gyarados if you nail it on the switch, while Heal Block is very useful against Snorlax which can be a nuisance if it manages to paralyse Virizion.
I'll wrap up with a change that is optional but which I think helps to fix some lingering issues. Your team is relatively slow with Mega Houndoom being the fastest Pokemon at 115, and lacks any method of speed control. Bronzong is your only switch-in to Dragons which usually carry coverage moves to beat it. Finally, a well-played Sableye is a huge threat to your team since it is potentially able to stall out everything on your team apart from Mega Houndoom, which faces a lot of trouble against Snarl versions. So a nice option to solve this would be to try out
Whimsicott over Virizion. Whimsicott retains Virizion's ability to absorb Dark attacks and check Waters while adding useful additional resistances to Fighting and Dragon. A standard moveset of Moonblast / Giga Drain / Stun Spore / U-turn would offer your team so much: paralysis support, a pivot, a check to Dragons and Sableye, and an amazing last ditch option against sweepers like Double Dance Cobalion and DD Mence. While Lum Berry Virizion is admittedly a better check to Suicune, running Acid Spray on Tentacruel means that Whimsicott can still check Suicune decently enough. The main downside is that you become a lot weaker to Snorlax without Virizion, so if you do want to try Whimsi out I would definitely go with
Heal Block on Bronzong to prevent Lax from resting up. You also lose an important wincon with this change, however Whimsicott has the speed and power to wreak plenty of havoc and is more than capable of delivering a sweep itself late-game with its STAB Moonblast. In the end though this is a change I'll leave up to you since your team can still function pretty well without it.
Summary
- Jellicent -> RestTalk Gyarados
- Tentacruel: Sludge Bomb + 252 HP / 252 Def / 4 SpD -> Acid Spray + 240 HP / 244 Def / 24 Spe
- Bronzong: Gyro Ball + 192 HP / 252 Def / 64 SpA Relaxed -> Heavy Slam + 252 HP / 168 Def / 88 SpD Careful
- Mamoswine: Expert Belt + Superpower -> Life Orb + Knock Off
- (Optional) Virizion -> Whimsicott, Bronzong: HP Electric -> Toxic / Heal Block
Great job with the team and I hope my suggestions help!