Roselia was a rather forgettable gen 3 single stage evolution that lacked both casual and competitive appeal, and whose only real claim to fame was as Drew's signature contest Pokemon from the anime. But gen 4 gave the forgettable flower a new interest and lease on life no thanks to an adorable pre-evolution and especially a new evolution.
From a bland rose branch to a design that draws inspiration from bouquets, masquerade balls, masked swordsman like Zoro, and you could even see some kunoichi elements to its motif! And thanks to a boost to its speed and special stats, access to nifty status moves, and not to mention a few cool abilities to play around with, Roserade finally has some competitive value to it as well. That said, it still lacks defenses, it's speed isn't too high compared to other threats, and it's movepool is not wide outside its STAB. But this floral fighter still has much to offer in many fields of elegance and domination. If it's good enough for your gen 4 rival and Cynthia herself, it's good enough for you!
Killer Kunoichi
Ability: Natural Cure/Poison Point
Item: Black Sludge
Nature: Timid
EVs: (HP 252) (Sp. Att. 252) (Speed 252)
Moves:
Sleep Powder
Toxic Spikes
Venoshock
Giga Drain
Set Details:
A status abuser befitting a skilled female ninja. Put your target to sleep with Sleep Powder, start laying down Toxic Spikes for itself and teammates, hit poisoned targets with Venoshock that doubles in power against said targets, and your back up STAB offers both consistent damage and a means to recover off damage yourself. Invest your stats into special attack but mostly speed, slap on Black Sludge for extra survivability, and Natural Cure is good for shaking off status effects with a quick switch, though Poison Point may help synergize with Venoshock if you are lucky.
Sunny Day Debutante
Ability: Natural Cure
Item: Life Orb
Nature: Timid
EVs: (HP 252) (Sp. Att. 252) (Speed 252)
Moves:
Sunny Day
Solar Beam
Sludge Bomb
Weather Ball
Set Details:
This lovely lady will bring sunshine to your day... and rain poison and hellfire onto other suitors. Set up Sunny Day and suddenly your Solar Beams become spamable one-turn attacks and Weather Ball becomes a powerful Fire type coverage move. Round things out with your secondary STAB Sludge Bomb with its cool 30% poison rate and you hit most targets for neutral damage between the three attacks. Max special attack and speed again, Natural Cure for peace of mind against status wielders, and this time put on Life Orb to grant some much appreciated damage.
Zoro's Zeal
Ability: Technician
Item: Life Orb
Nature: Jolly
EVs: (HP 252) (Att. 252) (Speed 252)
Moves:
Swords Dance
Power Whip/Bullet Seed
Poison Jab
Pin Missile
Set Details:
A surprise swordsman set that can throw off villains and competitive players alike. Set up Swords Dance to shore up your lackluster damage which will surprise your opponent who will expect a special attacking set. Power Whip offers consistent damage, but Bullet Seed is 100% accurate and in tangent with Technician as Roserade's ability it offers a means to break Substitutes and potentially inflict stronger damage than even Power Whip (2 hits = 75 damage, 3 hits = 112 damage, 4 hits = 150 damage, 5 hits = 187 damage). Poison Jab is the obvious secondary STAB with 30% poison rate, and Pin Missile is your best coverage option available that also benefits from Technician (See calculations from before). Maximize your stats in physical attack and speed, put on a Life Orb from before, and proceed to slash though the opposition.