Bat is a synonym of Cream. Cream is a synonym of Light. Light is related to Gentle. Gentle is the opposite of Mean. 
Growth is etymologically related to Grow. Mushroom is a type of Grow. 
Bat <--Synonym--> Cream <--Synonym--> Light <--RelatedTo--> Gentle <--Antonym--> Mean 
Growth --EtymologicallyRelatedTo--> Grow <--IsA-- Mushroom 