This is a new theory that i have made based on this new info: The Curse of the Shadow Devil is that is cause your own inner evil, the "Shadow" of your self to take over, but its not strong enough to make them 100% pure evil but the inner evil that is in all of us. Taichi did not want to take over the world of Kung Fu or anything before the curse, he just wanted to prove that he was stronger than Chen, but with the curse, his personality was changed and he became a more evil version of himself, and i belive that the now comming Dark pets where under the effect of the Shadow Devil curse, but they where purified in a way when they are summond by the player, but only so that they are not evil and loyal to the now evil Taichi, but their bodies and some of their personalities are not changed... Like Backarachnia from Best Wars, she joined the Maximals, but she remaind with her Predacon program... that is until her Upgrade into her Transmetal 2 form, but thats not important.