To combine the aesthetics, start with the characters. Red Alert has soldiers in military uniforms. They could be given some elements of Inferno's style, like having a small infernal symbol on their helmets or a bit of his fiery energy running through their weapons. For the vehicles, instead of just the normal metal look, they could have a molten look around the edges, as if they've been in contact with Inferno's world. The sky in the combined universe could be a mix of the smoky, war - torn sky of Red Alert with some of the strange, otherworldly colors that are often associated with Inferno's world, creating a really unique and visually striking atmosphere.
The armor and weapon designs can be merged. Dovahkiin's iconic dragonplate armor could inspire new skins or even new item designs in League of Legends. The weapons, like the dragonbone warhammer, could be reimagined as a powerful weapon for a champion in the game, with similar aesthetics but adapted to fit the game's balance.
Well, in terms of the aesthetics, the dark and gloomy atmosphere of Resident Evil can be enhanced with the more neon - like, glowing elements of the Black Light. For example, infected areas could have a strange mix of the Resident Evil's dilapidated buildings and the Black Light's glowing veins running through the walls.
You can start by establishing a crossover point. Maybe there's a special place that exists in both universes at the same time, like a hidden dimension. Characters from both the Danny Phantom and alicorn universes could discover this place accidentally. Then, you could introduce a concept that ties the two together, like a prophecy that involves a Danny Phantom character and an alicorn. This would give a reason for them to team up and explore each other's worlds. Also, having some shared rules for magic and power - related things in both universes can help in making the combination more seamless.
One way could be through a magical portal. Maybe some Fairy Tail magic creates a portal that sucks Naruto and his ninja friends into the Fairy Tail world. Then they have to team up with the Fairy Tail mages to face a common enemy.
In a fanfiction, the ideologies of the two universes could also clash or merge. The Gundam universe often deals with themes like war, peace, and the morality of using advanced weaponry. In Attack on Titan, it's about survival, freedom, and the mystery of the Titans. A fanfic could explore how characters from both sides react to these different concepts.
One way could be through a magical portal or rift that causes the magic from both universes to mix. For example, Natsu's fire magic could be affected by the dark and mysterious magic of the Black Bird world, making his flames have new properties. Maybe they turn purple or have the ability to nullify certain types of magic from the Black Bird world.
One plot idea could be that Inferno, a character from one universe, somehow gets transported to the Red Alert universe. He could find himself in the middle of a war between the Allies and the Soviets. Maybe he initially tries to stay neutral but then realizes he has to take a side to survive. Another idea is that he teams up with a Red Alert character who has a similar power or goal, like a psychic soldier, and they combine their strengths to face a common enemy that threatens both their worlds.
Well, it could be that the magic from Harry Potter's world and Android 18's advanced technology somehow interact. Maybe the spells in Harry Potter are used to enhance or modify Android 18's abilities. For example, a spell could be cast on her to make her energy blasts more powerful or her speed even faster.
Another aspect could be the fusion of their worlds' elements. In Mortal Kombat, there are dark and hellish realms, while Naruto has its own unique elemental chakra system. A fanfiction could explore what would happen if the dark magic from Mortal Kombat's realms seeped into the Naruto universe and affected the chakra. Maybe it could create new types of jutsu or even corrupt some of the ninja. It would be a great source of conflict and adventure in the story.
Maybe a character from the Naruto universe, like Naruto himself, could be summoned to Wakanda due to some powerful magic or technology gone wrong. He would bring his ninja skills and values, and his presence could disrupt the power balance in Wakanda. This would lead to various interesting scenarios, such as Naruto learning about Wakandan culture and the Wakandans learning about ninja techniques.