script.js

let headGear = [
	'minecraft:leather_helmet',
	'minecraft:iron_helmet',
	'minecraft:golden_helmet',
	'minecraft:diamond_helmet'
]

let chestGear = [
	'minecraft:leather_chestplate',
	'minecraft:iron_chestplate',
	'minecraft:diamond_chestplate'
]

let legGear = [
	'minecraft:leather_leggings',
	'minecraft:iron_leggings',
	'minecraft:golden_leggings',
	'minecraft:diamond_leggings'
]

let feetGear = [
	'minecraft:leather_boots',
	'minecraft:iron_boots'
]

var maxHead = headGear.length;
var maxChest = chestGear.length;
var maxLegs = legGear.length;
var maxFeet = feetGear.length;

onEvent('entity.spawned', event => {

	var world = event.getWorld()
	var entity = event.getEntity()

	if (entity.getName() == 'Skeleton') {

		var random = utils.getRandom().nextDouble()

		var randomHead = utils.getRandom().nextInt(maxHead)
		var randomChest = utils.getRandom().nextInt(maxChest)
		var randomLegs = utils.getRandom().nextInt(maxLegs)
		var randomFeet = utils.getRandom().nextInt(maxFeet)

		// 10% chance to spawn with iron_pickaxe & random armor from gear lists
		if (random <= 0.1 && entity.getRidingEntity() == null && entity.getY() < 64) {

			entity.setMainHandItem(Item.of('minecraft:iron_pickaxe'))

			entity.setHeadArmorItem(Item.of(headGear[randomHead]))
			entity.setChestArmorItem(Item.of(chestGear[randomChest]))
			entity.setLegsArmorItem(Item.of(legGear[randomLegs]))
			entity.setFeetArmorItem(Item.of(feetGear[randomFeet]))

		} else if (random <= 0.5) {
			// 40% chance to spawn with bow enchanted with power 4
			entity.setMainHandItem(Item.of('minecraft:bow').enchant('minecraft:power', 4))

			entity.setHeadArmorItem(Item.of(headGear[randomHead]))
			entity.setChestArmorItem(Item.of(chestGear[randomChest]))

		}
	}
})