replaceitem

/scoreboard objectives add target dummy

/scoreboard players set @e[type=Zombie] target 1

/scoreboard players set @e[type=Skeleton] target 1

/scoreboard players set @p target 1

/scoreboard players reset *

/replaceitem entity @e[score_target_min=1] slot.armor.head minecraft:golden_helmet

/replaceitem entity @e[score_target_min=1] slot.armor.legs minecraft:leather_leggings

/replaceitem entity @e[score_target_min=1] slot.armor.chest minecraft:diamond_chestplate

/replaceitem entity @e[score_target_min=1] slot.armor.feet minecraft:iron_boots

/replaceitem entity dragnoz slot.inventory.10 minecraft:iron_sword

/replaceitem entity @e[score_target_min=1] slot.armor.head minecraft:air

http://www.dragnoz.com/chaning-armour-on-entities-with-replaceitem-youtube/