Maybe an outside force, like a neighboring land that wants to conquer the Land of Snow for its strategic location or valuable resources. They send in their best warriors and ninjas to take over, and Naruto has to defend the land and its people.
A group of bandits who have made the Land of Snow their base. They constantly raid the villages and Naruto has to stop them. These bandits could have some sort of special ability related to the cold environment, like being able to blend in with the snow or use ice weapons more effectively than normal people.
It could be an ancient demon that was sealed away long ago in the Land of Demons but has now broken free. This demon could be extremely powerful and have a vendetta against the ninja world.
There could be a powerful shinobi from within Konoha who is jealous of Naruto's unique ability to control snow. This shinobi might secretly work against Naruto, trying to undermine his progress and steal the power for himself.
A rogue group of transformed dinosaurs that have lost their sense of morality due to the transformation could be the main antagonists. They might use their new powers to take over the best feeding grounds and force the other dinosaurs out.
It could be a powerful dark wizard who has found a way to control the forces in the Land of the Dead. Maybe he was once a student at Hogwarts who delved too deep into the Dark Arts and now wants to use the power of the dead to rule the wizarding world.
It could be someone from the Naruto universe who doesn't like Naruto's newfound fascination with Aku. For example, Danzo might see Naruto's interest in Aku as a threat to the stability of the village and try to stop Naruto from further exploring Aku - related things. So, Danzo could be the main antagonist in this case.
Maybe a new character could be introduced as the main antagonist. This character could be from a hidden village that has been secretly observing Naruto's growth. They realize his potential as a weapon and plan to steal his power or use him to start a war against other villages.
Krampus himself could be the main antagonist. Since he is a figure known for punishing the naughty, his actions in the Naruto world might be seen as unjust. He could be going after ninjas without really understanding their motives, causing a lot of trouble for the main characters.
It could be a rogue ninja who also has somehow acquired bankai - like powers. This antagonist might be jealous of Naruto's newfound abilities and wants to prove that he is the stronger one. So he starts causing chaos in the ninja world, challenging Naruto at every turn.
It could be a rogue ninja who wants to disrupt Naruto's business to gain power. Maybe he's jealous of Naruto's success and popularity in the business world. He could try to steal Naruto's business secrets or sabotage his operations.
It could be a rogue Kumo ninja who is jealous of Naruto's power and wants to prove himself by defeating Naruto. This ninja might have some dark secrets and a grudge against Kumo as well.