Mutate

Mutation occurs when a creature has the right stats and is high enough level, upgrading from Baby to Champion and then becoming a Legendary

Most Creatures only have one Legendary mutation while the other side of their upgrade tree only has a Champion.

The only exceptions to this rule are Toru and Ziel

the necessary upgrades for each beast goes as follows, and is listed in the Guide

Stymph:

Path 1: Uses Attack Upgrades to become Szamora

Path 2: Uses Intelligence upgrades to become Slyph, who can then use a mixture of Attack and Intelligence upgrades to become Stymphalin

Seph:

Path 1: Uses Health upgrades to become Syngard

Path 2 uses Strength upgrades to become Sydra, who can then use Attack and Agility Upgrades to become Valindra

Toru is one of 2 beasts who has Legendary paths

Path 1: Toru can use Strength to become the champion Tortle, who can upgrade to Kristle using Attack and Strength

Path 2: Toru becomes Toruga by Upgrading Health, and Toruga becomes Garuga by upgrading Strength and Health

Ziel is the other beast with 2 Legendary paths.

Path 1: Ziel becomes Carac by upgrading Strength then upgrade Strength and Attack to become Carpace

Path 2: Ziel becomes Thundra by upgrading Agility then upgrade Attack to become Thunduga

Rog:

Path 1: Rog becomes Grolum by upgrading Health then upgrade Strength and Health to become Groking

Path 2: Rog becomes Rogul by upgrading Strength

Petal:

Path 1: Petal can become Silkleaf by upgrading Intelligence and further upgrading Intelligence and upgrading Attack Mutates it into Jolkleaf

Path 2: Petal becomes Vinedos by upgrading Attack

All the following Beasts have one path

Havok:

upgrading Intelligence on Havok mutates it into Kavoc and upgrading Agility and Strength after that mutates it into Kravall

Durg:

Upgrading Health mutates Durg into Durgo and further upgrading Attack and health mutates it into the fearsome Disturbo

Gargo

upgrading attack mutates Gargo into Gargle and upgrading attack and agility further mutates it into Gargole