I'm trying to create a relatively balanced fire/water/grass core team that covers most prominent bases.
Here's what I've come up with:
Rillaboom @ Choice Band
Ability: Grassy Surge
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Knock Off
- Grassy Glide
- U-turn
- Wood Hammer
Garchomp @ Life Orb
Ability: Rough Skin
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Swords Dance
- Earthquake
- Scale Shot
- Fire Fang
Garchomp is carrying Fire Fang because Heatran is already setting up Stealth Rock for me, and Stone Edge is okay but it's only been really great against something like Togekiss. Earthquake/Scale Shot covers basically everything else. + w/ Fire Fang it's more difficult for Ferrothorn/Corviknight to wall me.
Suicune @ Leftovers
Ability: Pressure
EVs: 252 HP / 228 Def / 28 SpD
Calm Nature
- Calm Mind
- Scald
- Toxic
- Rest
I love this set. It's both physically and specially defensive after a calm mind or two, and I've been able to spam calm mind to +6 a lot because my opponent couldn't do enough damage to KO before I rest, and even pulled off a few sweeps with it, despite this not being a sweeper set. Special attackers for the most part are completely walled and a lot of physical attackers have to set up before they can deal significant damage, but that gives me a chance to go for a burn.
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 76 SpA / 128 SpD / 52 Spe
Modest Nature
- Stealth Rock
- Magma Storm
- Dark Pulse
- Earth Power
Heatran is running Dark Pulse because I opted for more coverage rather than running taunt or something of that nature.
Dark Pulse doesn't particularly do a whole lot but I've caught a few Dragapults slacking with it.
No other moves particularly do a whole lot either, including Taunt. Let me know if there's a better one.
I honestly don't think Heatran fits on my team that well, but I don't know of a better fire type, + stealth rock is always nice.
Melmetal @ Choice Band
Ability: Iron Fist
EVs: 48 HP / 252 Atk / 4 SpD / 204 Spe
Adamant Nature
- Double Iron Bash
- Ice Punch
- Earthquake
- Superpower
The 48 HP is to survive an Earthquake from a potentially banded Landorus-T and reply with Ice Punch for an easy (usually) OHKO.
Zapdos @ Heavy-Duty Boots
Ability: Static
EVs: 248 HP / 220 Def / 40 Spe
Timid Nature
- Volt Switch
- Roost
- Heat Wave
- Defog
A major weakness I've noticed is that I rely waaaaaay too much on Melmetal to take out some common threats such as Tyranitar, Landorus-T, Blissey/Chansey, amongst others. Garchomp can handle these more or less providing it gets a chance to set up, but I'm not trying to gamble on whether or not I'll be able to safely do that.
Rillaboom can take on Tyranitar and situationally Landorus-T as well but more often than not it's been safer to do it with Melmetal.
I think I rely too much on Melmetal in general though. It's been the sole reason I've been able to win >60% of the times when I've won.
Another one is that the team struggles pretty hard against Corviknight.
Corviknight itsself doesn't seem to do a whole lot to my team but I don't really have a solid answer to it.
It usually ends with me having to shuffle my team around a lot until I'm given a chance to finish it off.
There are probably more but those are the one's I've noticed thus far.
Here's what I've come up with:
Rillaboom @ Choice Band
Ability: Grassy Surge
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Knock Off
- Grassy Glide
- U-turn
- Wood Hammer
Garchomp @ Life Orb
Ability: Rough Skin
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Swords Dance
- Earthquake
- Scale Shot
- Fire Fang
Garchomp is carrying Fire Fang because Heatran is already setting up Stealth Rock for me, and Stone Edge is okay but it's only been really great against something like Togekiss. Earthquake/Scale Shot covers basically everything else. + w/ Fire Fang it's more difficult for Ferrothorn/Corviknight to wall me.
Suicune @ Leftovers
Ability: Pressure
EVs: 252 HP / 228 Def / 28 SpD
Calm Nature
- Calm Mind
- Scald
- Toxic
- Rest
I love this set. It's both physically and specially defensive after a calm mind or two, and I've been able to spam calm mind to +6 a lot because my opponent couldn't do enough damage to KO before I rest, and even pulled off a few sweeps with it, despite this not being a sweeper set. Special attackers for the most part are completely walled and a lot of physical attackers have to set up before they can deal significant damage, but that gives me a chance to go for a burn.
Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 76 SpA / 128 SpD / 52 Spe
Modest Nature
- Stealth Rock
- Magma Storm
- Dark Pulse
- Earth Power
Heatran is running Dark Pulse because I opted for more coverage rather than running taunt or something of that nature.
Dark Pulse doesn't particularly do a whole lot but I've caught a few Dragapults slacking with it.
No other moves particularly do a whole lot either, including Taunt. Let me know if there's a better one.
I honestly don't think Heatran fits on my team that well, but I don't know of a better fire type, + stealth rock is always nice.
Melmetal @ Choice Band
Ability: Iron Fist
EVs: 48 HP / 252 Atk / 4 SpD / 204 Spe
Adamant Nature
- Double Iron Bash
- Ice Punch
- Earthquake
- Superpower
The 48 HP is to survive an Earthquake from a potentially banded Landorus-T and reply with Ice Punch for an easy (usually) OHKO.
Zapdos @ Heavy-Duty Boots
Ability: Static
EVs: 248 HP / 220 Def / 40 Spe
Timid Nature
- Volt Switch
- Roost
- Heat Wave
- Defog
A major weakness I've noticed is that I rely waaaaaay too much on Melmetal to take out some common threats such as Tyranitar, Landorus-T, Blissey/Chansey, amongst others. Garchomp can handle these more or less providing it gets a chance to set up, but I'm not trying to gamble on whether or not I'll be able to safely do that.
Rillaboom can take on Tyranitar and situationally Landorus-T as well but more often than not it's been safer to do it with Melmetal.
I think I rely too much on Melmetal in general though. It's been the sole reason I've been able to win >60% of the times when I've won.
Another one is that the team struggles pretty hard against Corviknight.
Corviknight itsself doesn't seem to do a whole lot to my team but I don't really have a solid answer to it.
It usually ends with me having to shuffle my team around a lot until I'm given a chance to finish it off.
There are probably more but those are the one's I've noticed thus far.
Zapdos is a great answer to Rillaboom and Kartana that could be huge threats for your team otherwise. However I think that Mandibuzz 
would bring more utility here as it is also able to check Rilla and Kart while being a Defoggers and a Pivot. But Mandibuzz also gives you a reliable answer to Dragapult and an anti-setup option with Foul play. Indeed, Mandibuzz is better than Zapdos to deal with mons like Swords Dance Garchomp. Here is a spread of Mandi that make him able to check both Specs Dragapult and Rilla/Kart:
Garchomp is a good choice here. However, I think you’ll benefit more from a defensive variant here. Defensive Garchomp with the Grassy Terrain support is really good, giving you a reliable Heatran answer and being able to cheap a lot of physical threats with both Rough Skin and Rocky Helmet. Moreover, having Stealth Rocks on Chomp will free one move slot for Heatran which can be very useful to trap more efficiently annoying mons. The Garchomp’s set I’m thinking of is just below. You could also consider playing a Rocks offensive variant if you want to have an offensive Garchomp instead. (Also Scorching Sands could be an option over Earthquake).
Suicune can act as a wincon being able to slowly sets up and sweeps a lot of teams. However, I don’t think Toxic and Rest are good choices of moves here. Protect with Leftovers and the Terrain seems to be a better choice than Rest in order to recover. Thus, you should use Substitute over Toxic to avoid getting statued and completely wall some mons. I also think you need to have some speed on him, mainly to Sub before your opponent can act. Your Suicune set is an option that could work but I really think that a Sub Protect version can put more work here so don’t hesitate to try this. (Also, the spread may not be optimal, and you can try to play less Speed EVs and put them into Def).
Heatran acts here as a trapper and wall a lot of threats. To be more efficient in his trapping role and because Rocks are on Garchomp now, you can consider playing him with Taunt and Toxic. Taunt allow you to beat Blissey and mons using Teleport to escape. You could also Consider Protect as an option as it allows you to recover more health with both the Lefties and the terrain. Dark pulse is not good on Tran. It could be useful against Pult but as we have Mandi now there’s no need for it.
Banded Melmetal can be a good set here. However, you should use Thunder Punch instead of Ice Punch of this set as it will helps you dealing with Corviknight that can annoy the team and hurts mons like Toxapex and Slowbro as well. Ice Punch is a good option for Lando, but Lando already takes a ton of damage on Double Iron Bash and as it’s unable to recover you should be able to deal with him pretty easily. Another option for Melmetal is to use a Leftovers, Protect variant to benefit more from the terrain while being able to switch moves. I give you a set that you can try instead of the banded one If you want:
Not much to say here. Banded Rillaboom is a very good choice and the moveset is great. The only thing you should change is the nature going for Adamant instead of Jolly as you’re mainly clicking Grassy Glide on Faster mons and you’ll benefit more from an attack boost.
instead of Melmetal with a standard defensive spread. You will lose a lot of offensive power however, but Calm Mind Clef can still have some offensive presence. Here is the Clefable set to hesitate to also try with him in the team. Aromatherapy is also a great addition to heal Mandibuzz from any status and wake up Chomp if you used Rest.
