Aether

=Important Note=

The negative growth that scales with your challenge points only continues to scale until Aether is unlocked. Therefore, it is technically optimal to unlock Aether as soon into your game as is feasible. Ultimately, unlocking Aether is a judgement call to make. Be sure to plan around the Robot, Shark, Phoenix, Slime, and Bag's evo's.

Delirious Essence of the Forgotten
When you go into newbie ground with Aether Ring in your party items. It becomes stronger each time it is defeated. Each time it is defeated it will improve the pet Aether, raising its campaign gains and also giving it a growth bonus of 0.2*Total Challenge Points (Total at the time of fighting). You will need to defeat it 25 times to evolve Aether.