Go to Zanaris, making sure you have bought Fungicide spray first (1 charge per Zygomite).
Pick the fungi, and when it is almost dead, use the spray on it.
It sometimes drops Mort Myre fungi for filling Druid Pouch, or coins. They also can drop noted supercompost.
It uses magic attacks, so d'hide recommended.
mutated zygomite zygomites