I been wondering about that too. What is the reason for Ultra when there is no gain? I feel it's waste of time and pet snacks. I know pets are able to take certain jewels at Ultra but can we wizards save the hassle and make those jewels Mega?
Leveling up that high will not unlock any further talents for your pet, and the jewel you earn at Ultra will only give selfish talents.
Therefore, the only reason it's worth the effort of training up to Ultra, is if you already have a great ultra-level star jewel for your pet.
The only reason to raise a pet to Ultra is when you have a pet jewel (star) that you really want to use but can not add unless the pet is Ultra.
I never take a pet beyond Mega unless I want to add a jewel that requires Ultra. Even then, I only do it if I already have the jewel!
PS. Please note that 'Ultra Energy' can be equipped at Ancient. The word 'Ultra' is part of it's name, not it's requirement. Always check whether the jewel specifies it requires level Ultra before training further to use it. I took 2 pets to Ultra before finding out I could have added those jewels at Ancient! ROFL
you can equip an Ultra pet with an additional jewel. If you choose a jewel with a "selfish" trait, like Mighty, the damage or resist that your pet provides you with will be increased. KI is also selling gift cards with dual-trait jewels that do things like maycasts and increased pip chance.
So your awesome Mega Pet can be a little bit more awesomer as an Ultra Pet.