A new, evil sorcerer who has just arrived in Narnia could be the kidnapper. He might have heard tales of Lucy's importance and figure that by taking her hostage, he can control the forces of good in Narnia. Or perhaps a tribe of wild centaurs who have been corrupted by some dark magic might kidnap Lucy. They could be under the influence of a spell that makes them believe Lucy is the cause of all their problems and that getting rid of her will solve everything.
One possible kidnapper could be a rival engineer who is jealous of MacGyver's fame and ability to solve problems so effortlessly. This person might think that by kidnapping MacGyver, he can steal his ideas and take credit for his inventions. Also, it could be a group of eco - terrorists who believe MacGyver's work has been harmful to the environment in some way and want to force him to make amends by using his skills for their cause. A third option is a deranged fan who has an unhealthy obsession with MacGyver and wants to keep him all to himself, thinking that kidnapping is the only way to have MacGyver's undivided attention.
Perhaps a dark guild that has been observing Fairy Tail for a long time. They see Mirajane as a valuable asset and believe that her powers can help them in their evil plans. So they plot to kidnap her and force her to cooperate.
One idea could be that Lucy is kidnapped by an old enemy of Narnia who wants to use her as a bargaining chip to get something from Aslan. For example, they might demand that Aslan leave Narnia forever. Another plot could involve a group of dark creatures kidnapping Lucy because they believe she has a special power that they can harness for their own evil purposes. Maybe they think her connection to Aslan gives her some sort of magical energy that they can steal.
It could be a group of rogue shinobi from a neighboring village who are jealous of Konoha's power and see Hinata as a valuable hostage. They might think that by kidnapping her, they can gain some leverage over Konoha in terms of resources or territory.
A powerful and vengeful warlord from a forgotten realm could be a kidnapper. He might see Wonder Woman as a threat to his plans of conquest and decides to take her out of the picture by kidnapping her.
It could be a rival ninja clan if this is in a ninja - themed story. They might see Sakura as a valuable asset to get information about her own clan or to use her skills against her people.
Perhaps an old enemy of Igneel, Natsu's dragon father. They might see Natsu as a way to get revenge on Igneel. They think that by torturing Natsu, they can somehow hurt Igneel even though he's not around. Or it could be a group that is after the secrets of dragon slayer magic and believe Natsu has the key to unlocking those secrets.
Another possibility is a werewolf who has lost control or has a different agenda. In the Twilight universe, the werewolves and vampires have a tenuous relationship, and a werewolf kidnapping Bella could add a whole new layer of conflict. It could be a werewolf who doesn't trust Bella's relationship with the vampires and thinks she's a threat to their pack in some way.
Another possibility is some disgruntled former employees. Maybe they feel they were wronged by Stark and want to get revenge. They know his routines and weaknesses well enough to plan a successful kidnapping.
The Grimm could also be involved in an unusual way. Perhaps a new type of Grimm that has the intelligence to kidnap. They might be working with a human or Faunus villain who has some sort of control over them, and they take the character to an unknown location where the RWBY team has to face not only the Grimm but also the mastermind behind it.