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Insane vindicator with super speed, strength and damage. currently set as team "friendly" (change if you want to use it as a boss)

:D

Correct Command: /summon minecraft:horse ~ ~1 ~ {SaddleItem:{id:saddle,Count:1},Tame:1,Passengers:[{id:"minecraft:zombie",CustomName:"\"Knight\"",CustomNameVisible:1,HandItems:[{id:"minecraft:iron_sword",Count:1},{}],ArmorItems:[{id:"minecraft:iron_boots",Count:1},{id:"minecraft:leather_leggings",Count:1},{id:"minecraft:iron_chestplate",Count:1},{id:"minecraft:player_head",Count:1}],ActiveEffects:[{Id:14,Amplifier:0,Duration:2147483647}]}]}

If you want a mean boss? HERE YA GO!