Roserade @ Life Orb
Ability: Natural Cure
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Synthesis / Aromatherapy
- Sludge Bomb
- Leaf Storm / Giga Drain
- Spikes
I wanted to do Toxic Spikes Roserade, but it just didn't quite measure up. I figured Offensive Rade works well too. The moves are pretty obvious, the most prominent being Spikes, while Sludge Bomb gives it Fairy Coverage (good for Ampharos [ spoilers? ]) as well as Grass coverage if needed for those pesky... Chestnaughts? Sceptile maybe? It's still good STAB if Leaf Storm/Giga Drain won't cut it. Speaking of which, pick which one you think would work a little more efficiently for your team. Leaf Storm has intense power, threatening Gatr and Mega Swampert with KOs before finishing Set-up, but Giga Drain allows for more sustainability, which means more Spikes. That's also why Synthesis is on there, obviously. Though if Giga Drain is chosen: consider Aromatherapy for further team utility.
Max Speed is chosen to get Spikes up as Fast as possible and Max Special Attack allows Roserade's good Special Attack to become great, at the slight expense of bulk, though its amazing Special Defense is something to marvel at on its own.
Roserade also has insane synergy with Ampharos
Ampharos @ Ampharosite
Ability: Static
EVs: 132 HP / 252 SpA / 124 Spe
Modest Nature
- Thunderbolt
- Dragon Pulse
- Focus Blast / Hidden Power [Fire]
- Volt Switch
Ampharos itself is a really great Mega that is often overlooked because of the great number of Dragon and Ground Types which appreciate its typing and subpar speed. It forms amazing VoltTurn cores with mons like Darmanitan which pick up on its low speed and
While Amphy takes the Fire and Flying Types aimed at Roserade, Roserade easily cleans up most of the Ground Types and doesn't fear Florges. Krook is still a problem for both Pokemon, but unless it's Jolly Krook or a good prediction, Roserade does pretty well against it. The slow(ish) Volt Switch also means that Roserade is more likely to get in unscathed, allowing it to hit with more wiggle room, or to set up hazards on a mon that Ampharos just couldn't quite take care of.
The only move idea here is the idea of Hidden Power Fire. It allows this core to hit Steel Types a little harder (and more accurately) with the most notable being Forretress, who otherwise simply Spins unscathed against both. It does mean a little less coverage against Dark Types and Ice Types, but besides Krookodile and Mamoswine, I can't really think of one, and Ampharos shouldn't stay in on them anyways.