Well, Danny can go intangible, which means he could pass through solid objects. Spiderman could use this to his advantage. For example, if they are in a building surrounded by bad guys, Danny could phase through the walls and open doors from the inside for Spiderman to enter unnoticed. Also, Danny's flight ability combined with Spiderman's web - slinging could create a very unique form of transportation for them. They could quickly move across the city, with Danny flying and Spiderman swinging from Danny's body using his webs.
In a fanfiction, their powers could combine in really creative ways. Let's say there's a powerful electromagnetic - based villain. Danny's ectoplasmic body could disrupt the villain's electromagnetic fields as he is not fully of this physical world. Spiderman could then use his webs, which are conductive, to short - circuit the villain's power source. Danny's ability to overshadow people or objects could also be used in tandem with Spiderman's intelligence. Danny could overshadow a mechanical device and Spiderman could then remotely control it through Danny to do things like disable security systems or create distractions.
Well, in certain fanfictions, Danny's power of flight could be revealed to be much more than just floating in the air. It could be related to his emotional state. For example, when he's extremely determined or angry, his flight becomes faster and more powerful. This shows that his powers are not only physical but also tied to his emotions.
His powers could become more ice - based. Instead of the normal greenish - blue energy, his blasts might turn a frosty white. His ability to fly could also be affected, with a cold trail following him as he moves through the air.
His invisibility power would be extremely useful for stealth missions in RWBY. He could easily sneak up on Grimm or gather intelligence without being detected.
A fanfiction could also explore a scenario where Peter Parker gets some ghostly powers similar to Danny's due to an experiment gone wrong. He then has to learn how to control these new powers while still being Spiderman. Danny could come to help him understand and master these powers.
A Danny Phantom ice powers fanfiction could explore how his friends react to his new power. Sam and Tucker might be both amazed and a bit worried. They could help Danny test his powers in a safe environment, like an abandoned warehouse. And Danny might use his ice powers to create cool (pun intended) sculptures for fun, but also discovers that the power has a deeper connection to his family's ghostly heritage.
Well, often in fanfiction, Danny's powers evolve as he faces more powerful enemies. The need to defeat a stronger foe forces him to adapt and his powers change accordingly. For instance, he might develop the ability to phase through not just solid objects but also energy barriers. His ghostly wail, which was already a powerful weapon, could become more focused and destructive. Also, when he teams up with other powerful characters, their combined energies or knowledge can lead to his power evolution. They might teach him new ways to use his powers or unlock hidden potential within him. His power evolution in fanfiction is really diverse and depends on many different factors.
Spiderman's agility and web - slinging could be used to quickly move Power Girl around in battle, getting her to strategic positions. Her super strength could then be used to deliver powerful blows to enemies that Spiderman has trapped with his webs.
In Danny Phantom fanfiction, one interesting power could be enhanced ghostly strength. This allows Danny to overpower stronger ghosts than he could in the original series. Another power might be the ability to travel through different dimensions easily, opening up all kinds of new storylines and encounters. And sometimes, he has the power to manipulate time on a small scale, like freezing it briefly to avoid an attack or to get a better look at a situation.
The Joker would probably be both intrigued and excited. He might see Danny's powers as a new and interesting toy to play with. He could try to find ways to manipulate Danny into using his powers for the Joker's own chaotic purposes. For example, he might trick Danny into using his intangibility to break into a high - security building so the Joker can plant some crazy bombs or something.
Danny's powers could be a huge asset. His intangibility could help him and Batman get into places that are otherwise inaccessible. His flight would give them an edge in chasing villains across rooftops. Also, his ghostly energy blasts could be used as a new form of weapon against the bad guys in Gotham.