The gods in Warhammer 40k are on a whole different level of power. They can warp reality on a galactic scale. In Marvel, the Asgardian gods like Thor have great power, but it's not on the same scale as the Chaos Gods in Warhammer 40k. But if Thor were to face off against a daemon from Warhammer 40k, his lightning and strength might be enough to hold his own, especially if he had the help of some of his Marvel comrades and the technology and weaponry from Warhammer 40k.
Well, the races are very different. In Star Trek, you have the Federation races like Humans, Vulcans, and Klingons. They generally have a more diplomatic approach. In Warhammer 40k, races like the Orks are just out for a good fight all the time. So in a crossover, the Orks might see the Klingons as kindred spirits in a way, but the Klingons would probably be put off by the Orks' lack of honor.
In a Warhammer Naruto crossover, Naruto's Rasengan would be a very unique ability compared to the magic and melee combat in Warhammer. His ability to quickly form and launch a powerful ball of chakra could be devastating against many Warhammer foes. On the other hand, the Warhammer wizards' large - scale spells would be on a different level than most Naruto jutsus in terms of area - of - effect. For example, a powerful fireball jutsu might be like a small - scale version of a Warhammer fire spell.
One interesting idea could be a story where the Space Marines from Warhammer 40k team up with the Avengers. Picture the Ultramarines and Captain America leading a combined force against a chaos incursion in New York. The Ultramarines' discipline and advanced weaponry combined with the Avengers' superpowers would make for an epic battle.
Naruto's ability to create and manipulate chakra gives him a wide range of powers like the Rasengan and shadow clones. Compared to Marvel, it's somewhat similar to Doctor Strange's magic in terms of versatility. However, Strange's magic is more based on incantations and astral projection. Sasuke's Sharingan allows him to copy moves and predict attacks. This is a bit like Spider - Man's spider - sense in that they both help in combat anticipation, but the Sharingan is more about visual perception while the spider - sense is more of a sixth - sense feeling.
Superman's strength, flight, and heat vision are very powerful. In comparison, characters like Captain America in the Marvel universe have more of a combat and leadership skill set rather than superhuman physical abilities. However, Thor also has super strength and the ability to control lightning, which could be on a similar level to Superman's powers in some ways.
Ancient humans in Warhammer 40k fanfic can be very different from modern races. In terms of culture, modern races are often more fragmented and war - like. Ancient humans may have had a more harmonious society. They also might have had different physical capabilities. Maybe they were more resistant to the harshness of space without the need for bulky power armor like the Space Marines.
When it comes to power levels, Goku's Super Saiyan Blue form might be able to match up to Superman's full power. But Superman has the advantage of being able to fly in space without any issues, while Goku needs to hold his breath. Wonder Woman's combat skills are excellent, but they could be challenged by the martial arts expertise of the Z - fighters. And Martian Manhunter's telepathy and shape - shifting abilities would be a new kind of threat for the Dbz characters who are more used to straightforward physical battles.
Gohan's powers would be quite unique in the Marvel Universe. His Super Saiyan forms would give him a massive boost in power, far beyond what most normal Marvel characters can achieve without some sort of external boost. His Zenkai boosts, which increase his power after near - death experiences, could also be an interesting concept to introduce. And his martial arts skills, combined with his Saiyan instincts, would make him a very adaptable fighter against the various threats in the Marvel world. He could also potentially teach other heroes his fighting techniques.
It could be the Emperor of Mankind from Warhammer 40k. His psychic powers are off the charts and his influence over the entire Imperium is vast. He could easily manipulate the situation in a crossover. However, Master Chief from Halo also has his own set of skills and experience that make him a formidable opponent.
Sephiroth is extremely powerful with his superhuman strength, speed, and his iconic Masamune sword. In comparison, RWBY characters have their own unique abilities. Ruby has her speed and Crescent Rose. But Sephiroth's overall power level might be higher initially. For instance, his ability to fly and use powerful magic attacks would be a big advantage.