The question of how Shroomish obtain energy has often vexed researchers, for the ordinary methods are completely inapplicable in this case. Shroomish are not skillful battlers, so they are unable to hunt and gain experience in that manner, and even if they were, their forest homes are full of bug and flying pokemon which possess a type advantage against them. They are fungi, so they can not perform photosynthesis, although a plant in the dark forests they call home would find little light to nourish them either. Yet unlike most fungi, the shape of a Shroomish leaves them incapable of performing decomposition; their small mouth is useful only for shouting attack names.
Instead, Shroomish use special spores to drain energy and experience from the surrounding pokemon from a distance. These spores weaken the target's health to replenish Shroomish like Leech Seeds, but if the target is triumphant, they also transfer half the experience gained in battle to their master. Their spores can remain dormant for when Shroomish would benefit more from a champion than a meal,or they can be strengthened to make the host sleep even through a pokemon battle when a spore-carrier becomes too dangerous. Although Shroomish appear at constant rest, they are always commanding small armies of spores, activating and de-activating them to hasten their evolution.
Shroomish have no natural predators, for all have learned the folly of attempting to make them a meal. If one is slain, the spore which has fed the most blossoms into a new Shroomish, possessed of all the power and knowledge and spore network of their parent; the old Shroomish vanishes into dust. And yet they vanish often, as their hosts regard them as thieves; when they discover the parasitic spores they smash them and seek to regain their power through revenge.