One idea could be that Spiderman and Tigra team up to stop a new super - villain in the city who has the ability to control animals. They combine their skills, with Spiderman's web - slinging and agility and Tigra's feline strength and senses.
Perhaps there's a dimension - hopping plot where Spiderman and Tigra are accidentally thrown into different dimensions. They have to rely on each other to find their way back home while facing various threats unique to each dimension. Tigra's animal instincts help them navigate strange terrains and Spiderman uses his scientific knowledge to figure out the mechanics of the dimension - hopping.
Another plot could be that a powerful alien entity arrives on Earth and starts causing chaos. Spiderman and Tigra initially clash over how to handle the situation due to their different approaches. But as the threat grows, they realize they need to work together. Tigra's stealth and Spiderman's quick thinking form a great combination to outwit the alien.
A cool plot could be that a common enemy emerges, one that is immune to Spiderman's usual web - slinging and acrobatic combat, and also resistant to the Phoenix's raw power alone. So, Spiderman and the Phoenix - influenced character (it could be Jean Grey or someone else with Phoenix powers) have to combine their skills and minds to defeat this foe. They start off not getting along well, but as they face challenges, they learn to work together.
One idea could be that they team up to take on a new super - villain who has the ability to manipulate time. This would put their different skills to the test as they try to stop the villain from changing the timeline in a disastrous way.
One idea could be that the OC is a scientist who accidentally creates a device that can disrupt Spiderman's powers. This leads to a series of events where they have to work together to fix it while also facing off against a new villain who wants to use the device for evil. Another could be the OC is a new superhero in training and Spiderman becomes their mentor, and they develop a close bond as they fight crime together.
One plot idea could be that Spiderman gets transported into the Overwatch universe. He has to team up with the Overwatch heroes to stop a villain who has technology that can disrupt both universes. For example, Doomfist might be interested in using this technology to gain more power, and Spiderman's agility and unique powers would be useful in the fight.
One idea could be that The Vulture has a change of heart after Spiderman saves his life in a dangerous situation. He then decides to use his knowledge of technology to help Spiderman secretly against other villains. Another could be a story where they are forced to team up in an alternate dimension where they are the only ones who can stop a greater threat. A third idea is that The Vulture's daughter is in danger and Spiderman has to help him save her, which then leads to a strange alliance between them.
In a Venom x Spiderman fanfiction, a plot could involve Venom and Spiderman having to work together to stop a symbiote invasion from another dimension. The symbiotes from this other dimension are more aggressive and have different abilities. Spiderman has to use his intelligence and web - slinging skills, while Venom uses his brute strength and symbiotic powers. Along the way, they could start to understand each other better, and Venom could learn some of Spiderman's sense of responsibility. This would be a great opportunity for character development for both of them.
One idea could be that Venom and Spider - Man are forced to team up against a new symbiote villain that is far more powerful and malevolent. This new symbiote could be controlling innocent people, and Spider - Man and Venom have to find a way to stop it without harming the hosts.
One idea could be that they team up to fight a new villain who has the ability to manipulate time. This would put their different powers and personalities to the test as they try to stop the villain before he changes the timeline too much.
One idea could be a story where Spiderman has to team up with his greatest enemies to fight a new, more powerful threat from outer space. This would force him to put aside his differences and find common ground with the likes of Doctor Octopus and Green Goblin.
The Kingpin could be a great antagonist. He could be trying to take over more of the city and sees Spiderman and Tigra as threats to his plans. He uses his criminal network and his physical strength to try and stop them.