Perhaps a twist could be that the Reapers from Mass Effect are somehow related to the Chaos forces in Warhammer. This would completely change the dynamics of both universes. The Reapers' goal of harvesting organic life could be part of a larger plan by the Chaos to spread destruction across multiple galaxies. It would force the heroes of both worlds to team up in ways they never expected.
One interesting plot twist could be the combination of Mass Effect's biotics with Warhammer's psychic powers. Imagine a character who has both and has to learn to control this new, extremely powerful force. It could lead to a situation where they are feared and hunted by both sides of the crossover world.
One interesting plot twist could be the combination of Stargate's wormhole technology with Mass Effect's mass relays. Imagine if the two were somehow integrated, allowing for new travel routes across galaxies. Another could be characters from the two universes swapping abilities. For example, a Mass Effect character getting access to Stargate's Ancient technology and using it in unexpected ways.
A great plot twist might be that the Reapers from Mass Effect somehow end up in the Gears of War world. The Locust could initially see them as allies against the humans, but then the Reapers turn on them as well. It would create a chaotic situation where the Gears of War characters have to team up with some of the Mass Effect races they previously didn't trust to fight a common enemy that is far more powerful than anything they've faced before.
One interesting plot twist could be the combination of Call of Duty's military tactics with Mass Effect's alien races. For example, imagine soldiers from Call of Duty having to fight alongside the Krogan in a battle against a new, powerful enemy that has elements of both universes. Another could be the use of Mass Effect's biotics in a Call of Duty - like urban warfare setting. This would completely change the dynamics of combat as we know it in the Call of Duty world. And perhaps a plot twist where a character from one universe gets transferred into the other and has to adapt to a completely different set of rules and technologies.
A really cool plot twist could be that the Protheans, who are an ancient and advanced race in the Mass Effect universe, had actually encountered Cthulhu Mythos entities in the past. This could explain some of the mysteries surrounding their downfall and the disappearance of their technology. Maybe they tried to harness the power of these otherworldly beings and it backfired, leading to their civilization's collapse. This revelation would not only change how we view the Protheans but also add a new element to the overall lore of the Mass Effect universe.
In Warhammer 40k Mass Effect crossover fanfiction, a great concept is the mixing of combat styles. The high - tech weaponry of Mass Effect, such as the Omni - tools and assault rifles, against the brutal and often primitive - looking weapons of Warhammer 40k. It would be fascinating to see how a Mass Effect squad would fare against a horde of Orks. Additionally, the concept of different cultures' beliefs is interesting. The religious fanaticism in Warhammer 40k and the more scientific - minded approach in Mass Effect could create some intense ideological clashes.
One interesting plot twist could be that Fem Shepard is actually related to a powerful clan in the Naruto universe. This could be revealed through some sort of genetic discovery. It would completely change her understanding of herself and her place in both universes. Another twist could be that Naruto discovers he has latent biotic abilities that are only awakened when he is in the Mass Effect universe. This would give him a whole new set of powers to explore and master, and also create a connection between him and the technology - based world of Mass Effect.
In some fanfics, a plot twist could be that a Harry Potter character is actually a long - lost descendant of a powerful Sith. This completely changes the way they view their own magical abilities and heritage. Another interesting twist could be Mass Effect technology being introduced into the Harry Potter world, like biotic powers being mistaken for a new type of magic. It flips the normal understanding of both universes on its head.
One idea could be the Imperium of Man encountering the Citadel Council. The Imperium's strict dogma and military might would clash with the Council's more diplomatic approach. For example, the Space Marines might be seen as terrifying super - soldiers by the Mass Effect races.
One common theme is the clash of different cultures. The very different races in Warhammer and Mass Effect coming together often leads to interesting cultural exchanges and conflicts.
One interesting plot twist could be the combination of the Force from Star Wars with the psychic powers in Warhammer 40k. Imagine a Jedi using his Force powers in the grim and dark universe of 40k, facing off against Chaos psykers. Another could be the appearance of Imperial Stormtroopers in a Warhammer 40k battle, their white armor standing out among the chaos. Maybe they could be mistaken for some sort of new xenos threat at first. And a third plot twist might be the discovery of a lost Star Wars planet in the Warhammer 40k galaxy, full of unique technology and species that both sides would be eager to control or destroy.