Ultraman Taro: S1 E31 - Watch Out! The Lying Poison Mushroom Of Lies
A gigantic mushroom suddenly appears. It was defeated by Ultraman Taro, but a small mushroom that survived ends up in latchkey child Daisuke's mouth after being dared to eat it by some bullies. Once Daisuke becomes a mushroom person, he infests the water tower with mushroom poison and turns all of the complex's residents into mushroom people. Soon, even the ZAT members too!