Rotom-W, calm (special defense) nature with leftovers
HP and special def evs.
will-o-wisp, thunder wave, volt switch and hydro pump.
I usually lead with this guy. He doesn't really fit the sun theme I was going for, but I wanted a strong special tank that could switch in to take hard water and other special hits, as well as act as a status inflictor. Will-O-Wisp is there to take the punch out of physical attackers (and makes him able to tank them pretty well as well) while thunder wave is there for pokemon that can't be burned, as well as speed demons that need to be slowed, while hydropump is there to give him some offensive oomph. Volt switch is of course a great stab attack, and since rotom is a bit slow, allows him to absorb a hit and then switch in to another pokemon for free.
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Ninetails, Drought with a Heat Rock, Timid Nature (speed)
Max speed ev's, with a healthy dosing of HP and some special attack for seasoning.
Sunny Day, Will-O-Wisp, Fire Blast and Toxic
My sun setter. Sunny Day is there to help confirm that sun stays up, able to counter a rain dance or refresh the sun in the strange even that Ninetails remains in long enough for the sun to set. I don't expect her to last very long, she's mainly there to switch in when possible, and maybe poison or burn a pokemon along the way, while packing a powerful fire blast to avoid being made useless by taunt.
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Excadrill, Moldbreaker with Adamant (attack) nature, holding an air balloon. (EVs currently uncertain)
Rapid Spin, Earthquake, Rock Slide and Swords Dance
The other pokemon that doesn't really fit the sun theme, he's here purely because I needed a rapid spinner. Truth be told, I'm at a bit of a loss what to use him for other than that. He does have a nice electricity and poison immunity, as well as being able to switch in to take an earthquake for free up until his air balloon gets popped. Other than that, I've given him earthquake to use as a powerful stab attack, rock slide is there in case he gets stuck against a flying type (levitate won't stop him thanks to moldbreaker), and swords dance is there so that maybe he can pose a serious threat if he goes unchecked? This guy doesn't really inspire me all that much, I'm thinking about replacing him, maybe with a defogger since I don't run any hazards myself.
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Now for the pokemon I built this team around:
Venusaur, Chlorophyll with Life Orb, Timid (special attack) nature.
Special attack and speed ev's.
Growth, Giga Drain, Sludge Bomb and Sleep Powder.
This thing is an absolute beast. Under the sun, he's incredibly fast, and with life orb hits like a truck. Ideally, he'll come in when he's able to set up a growth, which gives him +2 to special attack if the sun is still out, with giga drain acting as his primary attack (which also negates the life lost through the life orb). Sludge bomb is his other super powerful stab attack, and obliterates fairies while covering the types that resist grass. Sleep powder is there to help secure a kill, set up a chance to use growth, or just give him a fighting chance if the sun is about to set, because his speed isn't that great outside of the sun (unless the foe is paralyzed, of course).
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Mega Charizard Y, modest with a charizardite Y, Solar Powered ability (though Drought when mega evolved)
Special attack and speed ev's.
Heat Wave, Solar Beam, Dragon Pulse, Focus Blast (or maybe roost?)
Two special sweepers? Why not. Mega Charizard Y doesn't need any setup under the sun, able to obliterate near everything with heatwave, while one-turn solar beams make short work of any water types that might try to oppose him, and focus blast is there for those super tanky normals. Dragon Pulse rounds out his type coverage, giving him an effective answer to dragons. If he can come in while the sun is still out, Solar Powered will still allow him to sweep with impressive power, while still keeping the ability to mega evolve to bring the sun back out if it sets. Because solar power is going to be sapping his health, I might replace focus blast with roost, but he's pretty fragile as is, so it might not make much difference.
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Trevenant, Impish behavior with Sitrus Berry, Harvest ability
Def and HP ev's with some attack thrown in to give him punch.
Leech Seed, Will-O-Wisp, Horn Leech and Shadow Claw.
I fucking love this thing. He acts as my physical defensive tank. Will-O-Wisp is there to make physical attackers even more useless while providing annoying, constant damage, and leech seed is always annoying while adding to his survivability. Horn Leech is a pretty powerful stab physical attack, with shadow claw for stab and type coverage. With leech seed and burn up, he's able to attack with horn leech and regain tons of health each turn, while also chipping away at tough opponents. Harvest gives him a 50% chance to recover his sitrus berry every turn, giving him even more health regen, and during sunlight that becomes a 100% chance. With his health regen and strong defense, he can even tank some super effective physical moves, with Rotom-W hopefully available to switch in and absorb any super effective special attacks sent his way.