Heidenröslein (Roselia) @ Eviolite
Ability:
Poison Point
EVs: 248 HP / 100 Def / 160 SpD
Calm Nature
-
Toxic Spikes
-
Venoshock
- Giga Drain
- Synthesis
This set is just for fun, and uses Roselia's other ability, Poison Point. With a high possibility of your opponent being Poisoned due to either Toxic Spikes or Poison Point, Venoshock doubles its base power and hits with 130 BP. Without any SpA, Venoshock can OHKO a poisoned Jumpluff.
252 Atk Jumpluff Acrobatics (110 BP) vs. 248 HP / 100 Def Eviolite Roselia: 218-260 (71.9 - 85.8%) -- guaranteed 2HKO
0 SpA Roselia Sludge Bomb (Venoshock) vs. 0 HP / 4 SpD Jumpluff: 290-344 (99.6 - 118.2%) -- 93.8% chance to OHKO
^(Sludge Bomb's Power is 130 here, because Venoshock doesn't exist in the calculator)
The 100 EVs in Defense let it survive a +2 LO Knock Off from Leafeon, and in return, Venoshock (if Leafeon is poisoned) also OHKOs.
+2 252 Atk Life Orb Leafeon Knock Off (97.5 BP) vs. 248 HP / 100 Def Eviolite Roselia: 256-302 (84.4 - 99.6%) -- guaranteed 2HKO
0 SpA Roselia Sludge Bomb (Venoshock) vs. 0 HP / 0 SpD Leafeon: 398-470 (146.8 - 173.4%) -- guaranteed OHKO
Alternatively, you could run a 144 HP / 252 SpA / 112 Spe spread with Modest to capitalize on Venoshock's damage against Poisoned targets. If playing this Roselia seriously, I would combine this Roselia with other Pokemon who can learn Toxic, that way Flyers who normally dodge Toxic Spikes could be Poisoned as well. Similarly, I'd add Pokemon with strong Ground / Psychic attacks to remove grounded Poison types that would otherwise soak up Roselia's Toxic Spikes.