Metapods are Caterpies in their Metamorphasis state.

Technacally as they can use moves like harden and reflect they are 'active pokemon' but to be honest there a little bit useless. The moves are natural defenses to protect the Cacoon that Caterpie is in.

Metapods are Caterpies wrapped tight in hardened silk.
It has an 'immatation' eye that is used to proctect itself against potential predators. The caterpie inside can detect danger and use its moves it attacked but it cannot actually see through the eye.

Unless the caterpie evolves in a trainers care they will naturally attach themselves to tree branches away from the dangerous forest floor below.
If a caterpie evolves while with a trainer they are advised to take it to an incubation centre where the men and women at the centre will care for it untill it becomes a Butterfree.
Overall Metapods are pretty usless in battle so this is highly recomended.

Hope you like it