We just released the first integration of a new feature we call "xp reserve".
Allow you to stack xp when you play using fully maxed characters. You can then use that xp in "My Collection" (we'll add this function to the collection pro as well) to level up your evolving characters.
How it works:
Your xp reserve has a max capacity based on your current level using that formula: max xp = 500 + your level * 100.
Then the extra xp is added automatically to your reserve at the end of each battle when you play using maxed characters (similar as how xp is added directly to the evolving characters).
We are going to add various ways to get capacity increases and maybe ways to get more xp in the reserve directly
It's still an early implementation but we couldn't wait!