So, Carmen was a descendant of mermaids, when the gargoyle's were training Carmen, Carmen thought they were just helping her to understand her powers so she wouldn't bring ultimate destruction upon the world but the gargoyle had their plans.
In Short, Carmen could control water and Trystan could control fire. Carmen can speak and understand fish while Trystan had werewolves abilities, Carmen's power in comparison to the description of heaven, it's just the same and Trystan's in company to hell, there was no different, they were clearly the opposite of each other but there was a little tiny idea of love amongst them but the gargoyle's were scared that Lucifer would descend.
So, the gargoyle's just wanted to understand both parties powers so that they'll be able to suppress it.
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Back in heaven, Kyle saw what the gargoyle's were trying to do with his daughter was bad, so he breaked the force field between every portal and every realm in the world leaving the world in chaos but to the naked eyes nothing happened. The chief gargoyle saw this he initially didn't think of Kyle or Lucifer, he focused on Trystan and Carmen which led to another history.
Chapter nine.
MERMAIDS.