Saiga

Steven is a character of the day who appeared in Whichever Way the Wind Blows. He is a scientist who explained to Ash, Misty and Brock the evolution process of Gloom into Bellossom or Vileplume.

After Ash and his friends broke up the fighting between Vileplume and Bellossom the first time with Bayleef's Vine Whip, Steven ran up to them and thanked them for doing so. He explained to the group about Oddish's branched evolutions. When one set of Gloom evolved into Vileplume and another set into Bellossom, Steven gave the group masks so they wouldn't inhale their Stun Spore.

Steven deduced the fact that a giant tree that the Vileplume and Bellossom shared was the cause of their fighting. The tree was the only source of shade. Steven than explained that when the tree covers the area the Bellossom are in, they go to the Vileplume's side and vice-versa for the Vileplume going to the Bellossom's side, causing an infinite loop as they both need the sunlight.

Later, Steven warned Ash, Misty, and Brock about heavy winds heading their direction. Inside the laboratory, they noticed the winds caused Gloom to evolve into Vileplume and Bellossom. After the storm stopped, Steven went outside with the group and allowed the fighting to occur to prove that fighting doesn't solve anything.

Team Rocket appeared and tried to capture the brawling Vileplume and Bellossom but were Stun Spored. The trio went for the Vileplume and Bellossom that got along instead but were blasted off by Bayleef's Vine Whip. Steven saw that all of the Vileplume and Bellossom got along afterwards. He waved his goodbyes to Ash, Misty, and Brock.

(Source: Bulbapedia)