Well, it shows his humility. By hiding his skills, he's not seeking the spotlight, which is a sign of a humble character. This can attract other characters to him and make them trust him more easily.
One possible fanfic could involve a battle against a powerful villain. Nightwing might get injured while trying to protect Gotham. Batman then has to step in not only to defeat the villain but also to take care of Nightwing. He could use his advanced medical knowledge and resources in the Batcave to nurse Nightwing back to health.
Red Hood is another good option. The two have a complex relationship, and a crossover could explore their past grudges and how they might overcome them to fight a common enemy. It could also show how their different approaches to justice collide and then reconcile.
He might try to reason with kaldur. If Nightwing can make kaldur see that what he's doing is wrong or that there are better ways to achieve his goals, kaldur could let him go. Nightwing is known for his charisma and intelligence in such situations.
He might try to engage Slade in conversation. Nightwing is smart and could be looking for a way to psychologically get an edge over Slade. He could be probing for Slade's motives, hoping to find a way to turn the situation around. He might also be stalling for time, waiting for the right moment to make his move.
Batman is the most likely. He has a strong bond with Nightwing and would do anything to save him. His skills in combat and detective work would be crucial in finding and freeing Nightwing.
A possible plot could be Nightwing getting betrayed by a close friend or ally. Maybe they were framed for something they didn't do, and this led to their heartbreak. For example, if a fellow hero believed false rumors about Nightwing and turned against him, it would shatter his trust and break his heart.
Nightwing would initially be defiant. He's a highly trained fighter and detective in his own right. So, he won't cower in front of the Joker. He'll probably try to size up the situation, looking for any weaknesses in his captivity and the Joker's plan.
Nightwing is alive in the comics. He's had his share of challenges and close calls, but as of now, he continues to fight for justice and protect the people.
I think it would vary depending on the writer's perspective. If the writer wants to emphasize the importance of experience and training, then Nightwing might be more dominant. He has years of experience fighting crime in Gotham. On the other hand, if the focus is on raw power and the ability to adapt quickly, Spiderman could be the more dominant character. His powers give him a wide range of abilities that he can use in different situations.