How to summon the really hard to beat zombie! Perfect for a boss fight!
It has:
10000 HP (Yes, seriously)
Speed
Full thorns 3 and protection 5 netherite armour (As if it wasn't already hard enough)
Resistance 3
Sharpness 5 netherite axe
Command: /summon minecraft:zombie ~ ~ ~ {CustomName:"\"Armoured Zombie\"",Health:10000,Attributes:[{Name:"generic.movement_speed",Base:0.5},{Name:"generic.attack_damage",Base:10}],ActiveEffects:[{Id:11,Amplifier:2,Duration:99999},{Id:23,Amplifier:2,Duration:99999}],ArmorItems:[{id:"minecraft:netherite_helmet",Count:1,tag:{Enchantments:[{id:"minecraft:thorns",lvl:3},{id:"minecraft:protection",lvl:5}]}},{id:"minecraft:netherite_chestplate",Count:1,tag:{Enchantments:[{id:"minecraft:thorns",lvl:3},{id:"minecraft:protection",lvl:5}]}},{id:"minecraft:netherite_leggings",Count:1,tag:{Enchantments:[{id:"minecraft:thorns",lvl:3},{id:"minecraft:protection",lvl:5}]}},{id:"minecraft:netherite_boots",Count:1,tag:{Enchantments:[{id:"minecraft:thorns",lvl:3},{id:"minecraft:protection",lvl:5}]}}],HandItems:[{id:"minecraft:netherite_axe",Count:1,tag:{Enchantments:[{id:"minecraft:sharpness",lvl:5}]}}],Tags:["boss"]

Want it to have a boss bar? use this command after spawning it /bossbar add ArmouredZombieBossBar "Armoured Zombie"
The this command /bossbar set ArmouredZombieBossBar players @e[​tag=boss,name="Armoured Zombie"]

So if your ready, get geared up and fight!
Let me know if you beat it! And if you made a video about the boss, I would love to see! Just give me credit.