It could be an evil ninja who has also discovered the secret of the Crimson Saiyan God but wants to use it for destruction. He might be jealous of Naruto and see him as an obstacle to his plan of ruling the ninja world with this new power.
Well, it could be about Naruto somehow obtaining the power of the Crimson Saiyan God. Maybe he gets transported to a different dimension where Saiyan powers exist and through some crazy adventure, he merges his ninja skills with Saiyan abilities. He might then use this new power to protect his village from a greater threat than ever before.
It could be a rogue ninja who has somehow harnessed the power of the Crimson Avatar in a dark and corrupted way. This ninja could use his powers to try and take over the ninja villages, believing that the traditional ninja ways are weak. He might see himself as a new kind of leader, using fear and his overwhelming Crimson Avatar powers to rule.
It could be an evil ninja who has already made a pact with the Abyssal God and wants to use its power to take over the ninja world. He might see Naruto as a threat to his plans because Naruto has a natural connection to the god's power.
Maybe an ancient being that was sealed away long ago but has now been awakened due to Naruto's newfound power. This being has a natural hatred for those who can control lightning and sees Naruto as a threat to its plans of taking over the ninja world. It has the ability to manipulate shadows and uses them to counter Naruto's lightning attacks.
Perhaps an organization that views the 'god of illusions' as a threat to their plans for world domination. They might see the 'god's' influence over illusions as something that can disrupt their schemes. So they send their most powerful agents to take on the 'god of illusions'. This could lead to some epic battles in the fanfiction.
It could be an evil shinobi who has somehow managed to control or manipulate the God of Death's powers for his own malicious purposes. This shinobi might use the power to create chaos in the ninja world, like raising the dead and making them fight against the living.
It could be a rogue ninja who has also harnessed the power of a god of destruction. This ninja wants to use the power to rule the ninja world and Naruto has to stop him.
It could be a powerful ninja who is jealous of Naruto's new godly powers. He wants those powers for himself and will stop at nothing to get them.
It could be an old rival who has also gained some sort of dark god - like powers. For example, Sasuke could have been corrupted by a powerful dark force while seeking more power, and now he stands in Naruto's way as he tries to use his new god - like abilities for good.
It could be someone who is jealous of Naruto's newfound 'god of luck' powers. Maybe a rogue ninja who wants to steal that power for himself. He might constantly be plotting against Naruto, trying to find a way to take his luck away.