Who could be the main villain in a Miraculous Ladybug Cat Noir and Tom fanfiction?

It could still be Hawkmoth. Since he's always after the Miraculouses, he might find a way to turn Cat Noir evil and use him as a tool to finally get Ladybug's Miraculous. So Hawkmoth would be pulling the strings in the background while Cat Noir does his dirty work.

One idea could be that Tom discovers the secret identities of Ladybug and Cat Noir. He could then get involved in helping them protect Paris in his own unique way, like using his baking skills to create special treats that give them extra energy during battles.

There's a fanfiction called 'The Miraculous Origins'. It delves deeper into the backstory of the Miraculous. It explores how the Miraculous were created and how they came to be in the hands of the current holders. It's a long read but worth it for fans who want to know more about the lore of the Miraculous Ladybug Cat Noir universe.

A possible main villain could be a character from Ladybug's past who has discovered her identity and is using that knowledge to create chaos. They could be blackmailing her or trying to steal her Miraculous by setting up elaborate mysteries and traps for her to solve.

Hawkmoth is an obvious choice. His whole mission is to obtain the Miraculouses, and in a death fanfiction, he could succeed in a more devious way than in the original series, directly or indirectly causing Ladybug's death.

An evil alien warlord could be the main villain. This warlord could be bent on conquering Earth and other planets in the universe. He might see the Miraculouses as a threat and try to destroy Ladybug and Chat Noir first.

A new character could be introduced as the main villain. Maybe a corrupt police officer who turns to the dark side. He could use his knowledge of the law and the city's security systems to commit crimes and frame the Miraculous heroes. He would be a formidable opponent as he has insider knowledge.

One consequence could be a power imbalance in Paris. Since Ladybug's Miraculous is crucial for maintaining the balance against evil. If Cat Noir takes it, he might not be able to use it as effectively as Ladybug, leading to potential chaos as Hawkmoth could take advantage.

If Cat Noir steals Ladybug's Miraculous in a fanfiction, it could lead to a dark turn in the story. Maybe he's being controlled by an outside force. This would shatter the trust between them and change the whole dynamic of their fight against evil. The city would be in more danger as Ladybug is a key protector.

One possible plot could be that Hawkmoth manages to finally corrupt Cat Noir. He might start causing chaos in Paris, attacking Ladybug instead of helping her. Ladybug would then be in a difficult situation, having to either try to save her partner or defeat him to protect the city.