Updated:
1. Wear a block on your head
/give @s minecraft:diamond_block[equippable={slot:"head"}]Right-click to put it on. Slots are head, chest, legs and feet. To just put a block on someone right now, /item replace entity @s armor.head with minecraft:diamond_block also works (item replace).
2. A chestplate that glides
/give @s minecraft:diamond_chestplate[glider={}]Wear it and jump in mid-air to glide like an elytra, keeping full diamond armor. Firework boosts work too.
3. An elytra with armor
/give @s minecraft:elytra[attribute_modifiers=[{type:"minecraft:armor",amount:8,id:"mc:elytra_armor",operation:"add_value",slot:"chest"}]]Adds 8 armor, the same as a diamond chestplate. On 1.20.5 to 1.21.4 wrap the list as {modifiers:[...]}; on 1.21.1 and older the type is minecraft:generic.armor.
4. Match the icon
/give @s minecraft:diamond_chestplate[glider={},item_model="minecraft:elytra"]The inventory icon becomes an elytra; the worn look does not change (item model command).
Troubleshooting
- Not equipped on right-click: check the slot name.
- No gliding: wear it in the chest slot and jump while falling.
- Error: needs 1.21.2+; Bedrock cannot do this with give.
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