Silver: It secretes a sticky, drool-like honey. Although sweet, it smells too repulsive to get very close.Crystal: The smell from its drool-like syrup and the pollen on its petals is so bad, it may make opponents faint.Red: The fluid that oozes from its mouth isn't drool. It is a nectar that is used to attract prey.
Prof. Lotus' Notes: Gloom is based on the plant Rafflesia arnoldii a.k.a. the 'Stinking Corpse lily'. The plant got it's name because it smells like rotting flesh. Rafflesia is a parasite and it infects the plant host where a bud emerges. This has uncanny parallels to what happened to Oddish. The red discoloration of the leaves on it's head are also reminiscent to when plants are not getting nutrients, and this is because the parasite is leeching from the host Oddish. I suspect that the infected Oddish, Gloom, has two evolution lines because one is a scenario where the host cannot battle the infection, keeping it's susceptibility to spread the Parasite (Vileplume), and a line that was able to combat the Parasite and the healthy Oddish evolves to what it actually should have evolved into (Bellossom).
Gender Differences: Female Gloom have one large spot per bud, whilst males are covered in spots.