Who could be the main antagonist in a Green Goblin crossover fanfiction?

It could be a powerful demon lord from the Doom universe that has possessed a goblin king in the Goblin Slayer world. This combined entity would have the cunning and numbers of the goblins along with the raw power and dark magic of the demon lord. It would be a formidable foe for the Doom Slayer and Goblin Slayer to face.

It could be some of the pure - blood wizard families who have always looked down on goblins and consider them as inferior beings. They might oppose Harry's attempts to defend the goblin because it goes against their traditional views of the wizard - goblin hierarchy.

It could be a dark wizard who has a vendetta against goblins. This wizard might see goblins as a source of power or wealth and wants to enslave them. So when Harry tries to save the goblin, this dark wizard becomes the main obstacle.

If it's a crossover with Alice in Wonderland, the Queen of Hearts could be the main antagonist. The Queen might see Tinkerbell as an intruder and try to behead her. Tinkerbell would have to use her wits and magic to survive in the crazy world ruled by the Queen of Hearts.

Maybe an alien from the Green Lantern universe who has a vendetta against the Green Lantern Corps decides to target Naruto's world. This alien believes that by causing chaos in the Naruto universe, he can draw out the Green Lanterns and destroy them. He has powerful weapons and abilities that are a challenge for Naruto and his friends to overcome.

It could be a rogue ninja from a hidden village who has a vendetta against the Green Beast. Maybe this antagonist blames the Green Beast for something that happened in the past.

A possible main antagonist could be Aizen from 'Bleach' who somehow gains the ability to control the powers from Lucy's world as well. He could use this newfound power to try and take over both the Bleach universe and Lucy's world. His cunning and powerful abilities would make him a formidable foe for Lucy and the Bleach characters to face.

A new character could be created. This character could be a powerful slug - human hybrid who has been corrupted by the dark side of both worlds' powers. He wants to rule over both Naruto's world and Slugterra, believing that the two worlds should be united under his rule. He has the ability to use both ninja techniques and slug powers, making him a very difficult opponent to defeat.

Maybe an interdimensional warlord who sees Goku as a threat to his conquest plans and Lemon as a valuable asset. He would stop at nothing to capture them and gain their powers. He could have an army of minions from different dimensions, making it really challenging for Goku and Lemon to fight back. This antagonist would be very cunning, constantly devising new strategies to outwit our heroes.

Perhaps an ancient and evil ninja from a long - lost clan that was sealed away behind the gate. He resents the modern ninja world and wants to destroy it. He has unique and powerful jutsus that Naruto and his friends have never seen before.