Ever wanted to spawn mobs with custom armor and weapons? Well I'm going to teach you how!

How to spawn a mob with items in their hands:

/summon zombie ~ ~ ~ {HandItems:[{id:"minecraft:iron_sword",Count:1},{id:"minecraft:iron_axe",Count:1}]

The first item (minecraft:iron_sword) is in the mobs right hand and the other item (minecraft:iron_axe) is in the left hand.

How to spawn a mob with armor:

/summon zombie ~ ~ ~ {ArmorItems:[{id:"minecraft:diamond_boots",Count:1},{id:"minecraft:diamond_leggings",Count:1},{id:"minecraft:diamond_chestplate",Count:1},{id:"minecraft:diamond_helmet",Count:1}]}

For the armor, the order goes from Boots, to Legs, to Chest, to Head. DO NOT FORGET TO ADD THE ,Count:1 AT THE END OR IT WON'T WORK.

Cheers,
-Grim