Silus happens upon Roselia while the latter is fleeing Lyra. After battling it, both trainers throw Pokéballs at it, but it is unclear who's captured the Roselia. After a battle between Silus and Lyra, in which Silus is victorious, Roselia joins Silus on his journey.
Roselia is a small Pokémon with a light green body. Roselia has a leaf skirt and holds a rose on each of its hands, a red one in its right and a blue one in its left. Roselia has leaves extending from its shoulders like epaulettes, and a pointed streak of yellow extends from its neck down the forefront of its leaf skirt. Visible from the back is a small stretch of yellow coloration around its neck much like a collar. Roselia also has three thorns on top of its head. Since it is male, it has a shorter skirt.
Roselia seem to be peaceful Pokémon, but can attack fiercely with powerful poisonous attacks upon sensing danger.
Roselia normally fire sharp thorns (either Poison Sting, Toxic Spikes or Pin Missile, but the latter of the three rarely occurs) as a first offense, usually at wild Pokémon who try to steal its flowers. Roselia are also capable of launching some Powder-based moves to either inflict status problems on its foes (Sleep Powder, Stun Spore, or Sweet Scent) or to heal the status problems of itself and its allies (Aromatherapy). Roselia are also capable of knowing Petal Dance. Like most Grass-type Pokémon, Roselia can take in sunlight and focus it into a SolarBeam.
When a Pokémon with Poison Point is hit by a move that makes contact, there is a 30% chance that the attacking foe will become poisoned.
Counter Shield: Using either Magical Leaf or Toxic Spikes, Roselia can preform Counter Shield. He learned this during Silus's training with the Ghost Pokémon Master in Mimosa City. If the latter of the two moves is used, the Counter Shield can cause poisoning to all who come into contact with it.