When does Oddish evolve?

Answer 1

Oddish evolves into Gloom starting at level 21, and then Gloom can evolve either into Vileplume using a Leaf Stone, or into Bellossom using a Sun Stone.

Oddish is #43 in the National Pokedex, and was introduced in the Generation I Pokemon titles (Red, Blue, and Yellow) where it could be found in Red only on Routes 5-7, and in Red and Yellow on Routes 12-15, 24, and 25. In Generation VI (X and Y), it can be found on Route 6.