This one, for example: /give @p minecraft:diamond_axe{AttributeModifiers:[{AttributeName:"generic.attackSpeed",Name:"generic.attackSpeed",Amount:-2,Operation:0,UUIDMost:42373,UUIDLeast:163894}]} 1
No, not player heads. Custom heads.
Otto Kapanen
This one, for example: /give @p minecraft:diamond_axe{AttributeModifiers:[{AttributeName:"generic.attackSpeed",Name:"generic.attackSpeed",Amount:-2,Operation:0,UUIDMost:42373,UUIDLeast:163894}]} 1