Extra is related to Tax. Tax is related to Burden. Pill is a type of Burden. Pill is a type of Artifact. 
Offense is a synonym of Offensive. Offensive is related to Guard. Guard is related to Defensive. Defensive is related to Tower. 
Extra <--RelatedTo--> Tax <--RelatedTo--> Burden <--IsA-- Pill --IsA--> Artifact 
Offense <--Synonym--> Offensive <--RelatedTo--> Guard <--RelatedTo--> Defensive <--RelatedTo--> Tower 