Pets

in world code put:

var egg = (pets, mutations) => {
    let nameD, rarityD, descD, itemD, tierD = null, mutationsD = [], r = Math.random(), a = 0
    for (let pet of pets) {
        a += pet.chance
        if (r <= a) {
            nameD = pet.petName
            rarityD = pet.rarity
            itemD = pet.item
            break
        }
    }
    for (let mutation of mutations) {
        r = Math.random()
        if (r <= mutation.chance) {
            mutationsD.push(mutation.mName)
            tierD = mutation.tier
        }
    }
    api.sendMessage(myId, `You got a ${rarityD} ${nameD}`)
    descD = rarityD
    for (let m of mutationsD) {
        descD += "\n" + m
    }
    api.giveItem(myId, itemD, 1, { customDisplayName: nameD, customDescription: descD, customAttributes: { enchantmentTier: tierD } })
}

then in a code block put this:

const petsR = [
    { petName: "Dog", item: "Brown Paintball", chance: 0.45, rarity: "Common" },
    { petName: "Cat", item: "Yellow Paintball", chance: 0.45, rarity: "Common" },
    { petName: "Red Dragon", item: "Red Paintball", chance: 0.1, rarity: "Epic" },
]
const mutationsR = [
    { mName: "[Glowing]", chance: 0.05, tier: "Tier 1" },
    { mName: "[Golden]", chance: 0.01, tier: "Tier 5" },
    { mName: "[Radioactive]", chance: 0.001, tier: "Tier 2" },
]
egg(petsR, mutationsR)

u can edit this to add mutations, more pets, just make sure the pets chances add up to 1