Magic. Harry Potter, as the Master of Death, would bring his powerful magic to the RWBY world. His spells could be a new form of combat or defense against the Grimm. For example, the Stunning Spell could be used to immobilize Grimm, giving the RWBY characters an advantage in battle.
The power of the Deathly Hallows. The Elder Wand could make Harry an extremely powerful fighter in the RWBY world. The Resurrection Stone could potentially be used to communicate with fallen RWBY characters, like Summer Rose, and gain valuable information. And the Invisibility Cloak could be used for spying on Salem's forces or for sneaking up on Grimm unnoticed.
A new kind of magic. Harry as the Master of Death could introduce a different type of magic system compared to the existing magic in Middle - earth. His power over death might allow for some unique plot developments, like bringing back characters who have fallen in the battles of Middle - earth.
Well, in a RWBY fanfiction with Harry Potter as the Master of Death, one way it could work is through a cross - dimensional portal. Harry could be accidentally transported to the RWBY universe. His status as the Master of Death might give him unique powers there. Maybe he could use the Deathly Hallows' powers to combat the Grimm. For example, the Invisibility Cloak could help him in stealth missions against the Grimm, and the Elder Wand could enhance his combat abilities against powerful foes in RWBY.
Harry Potter's strong sense of justice could influence the Mandalorians. He has always fought against evil, and he could inspire the Mandalorians to take on more noble causes. Maybe he would encourage them to be more inclusive towards other species in the Star Wars universe, just as he has been inclusive towards different magical beings in the wizarding world.
Well, it could be about Harry coming back to life in a new and unexpected way. Maybe he returns with even greater powers, being the Master of Death. He might use his newfound state to fix all the wrongs in the wizarding world, like finally getting rid of all the remaining Death Eaters once and for all.
The Master of Death could potentially use his powers to bring balance to the Twilight world. In Twilight, there is a constant struggle between vampires and werewolves, and humans are often caught in the middle. Harry, with his knowledge and power, could try to create a more harmonious coexistence. He might use his power to ensure that vampires don't overstep their boundaries when it comes to preying on humans. He could also use his understanding of life and death to help the werewolves better control their transformations, which are often tied to the cycle of the moon. And all of this would be done while exploring the new and different magic or supernatural elements in the Twilight universe.
In a Witcher fanfiction, Harry as the Master of Death could become a sort of mentor to young Witchers. He could teach them about the different aspects of death and how to face it without fear. His ability to control death could also be used to study the dark magic and curses that are often associated with the monsters in the Witcher world. He might be able to reverse some of the more deadly curses or prevent the spread of dark magic that is harming the land and its people. Also, he could use his connection to death to understand the nature of the monsters better, as many of them are often related to death or the underworld in some way.
It could be really interesting. Maybe the Master of Death abilities would allow Harry to survive the dangerous situations in the Stargate universe, like going through the stargates to unknown planets and facing alien threats. He could use his magic along with the technology in the Stargate world.
Well, it could be that Harry has complete control over death. He might be able to bring back the dead, or at least communicate with them freely. Maybe he uses this power to right the wrongs of the wizarding world, like resurrecting those who died unjustly during the war. He could also use it to gain ultimate knowledge, as death is often associated with hidden secrets in the wizarding lore.
In such a fanfiction, we might see Harry Potter's magic blend with the spiritual energy of 'Bleach'. The Deathly Hallows could have new interpretations in the 'Bleach' setting. For instance, the Invisibility Cloak could be seen as a form of spiritual concealment. And his mastery over death might make him a sort of enigma to the characters in 'Bleach'. He could also learn about the different levels of souls in 'Bleach' and how they compare to the concept of death in 'Harry Potter'.
The story could develop in many ways. Harry might use his connection to death to access the spirit world in the Avatar universe more easily than others. This could lead to him discovering secrets about the origin of bending or the history of the Avatar. He could also use his Gryffindor courage to stand up against any form of oppression in the Avatar world. His skills in magic, combined with his new - found knowledge of the Avatar world, could make him a powerful force for good or, if misused, a great danger. As he interacts with the different nations and characters, he'd slowly change the dynamics of the Avatar world, all while dealing with his own identity as the master of death.