Animalia/YMMV

Complete Monster: The Creeper; before he arrived, all characters in the show had at least once displayed a softer side, and the worst you could get was greedy yet harmless tiger who beside having some jerk moments wasn't really evil. The Creeper, on the other hand, has no redeeming qualities, and is actually willingly trying to damage the Heart and Animalia for his personnal ambitions. His schemes included trying to start a war on Animalia, kidnap a child, and trick the protagonist and Livingstone in falling to their death when Livingstone offered to forgive him for his fault. As if it wasn't enough, he is also an Omnicidal Maniac wannabe...
Creepy Awesome: The Creeper, again. Despite being the nastiest character in the show, fans love him.
Ensemble Darkhorse: Iggy and Fuschia are both quite popular characters amongst the fans, the first for
Moral Event Horizon: the Creeper crosses it several times; Trying to start a war in Animalia, attempting to kidnap Echo, tricking Alex, Zoe, Livingston and Fuchsia into almost being blown away to their deaths by the wind of no return... pick your choice.
The Scrappy: Allegra, though she does get Hidden Heart of Gold moments.
The Woobie: Fuschia, for having to put up with Tyrannicus