In a crossover with Halo, Master Chief would be a great addition. His combat skills and strategic thinking could interact well with the large - scale battles in Supreme Commander. He could lead the UNSC forces against the massive armies in the Supreme Commander world.
If we consider a crossover with the Lord of the Rings universe, Aragorn could be a good fit. He's a noble leader and a skilled warrior. His presence could force the Boys to reevaluate their ideas about power and leadership, and he could also be a strong ally against any corrupted power - hungry characters from the Boys' world.
The Terraria Guide could be a great character to include. He has a lot of knowledge about the Terraria world, so in a crossover, he could be the one trying to figure out the new world they're in. For example, if it's a crossover with Terraria and Hollow Knight, he could study the strange bugs and lore of the Hollow Knight world.
If it's a crossover with Teen Wolf, Stiles would be a great character to include. His quick thinking and sarcastic nature would contrast well with the more serious Shadowhunters. He could also provide some unique insights into solving problems, especially when it comes to the werewolf aspects of the Teen Wolf world that the Shadowhunters might not be as familiar with.
One idea could be to cross Supreme Commander with a sci - fi RPG like Mass Effect. The Supreme Commander's advanced technology could be introduced into the Mass Effect universe, causing a stir among the various species. Maybe the protagonist has to figure out how to use the Supreme Commander's strategic resources to fend off a new Reaper threat.
The Spartans from Halo would also be great main characters in this crossover. Their super - human abilities and combat training would make them stand out in the Supreme Commander world. They could be the ones to teach the Supreme Commander forces about hand - to - hand combat and stealth operations, which are not as emphasized in the Supreme Commander gameplay.
You could include characters like Harry Potter. His knowledge of magic from the Hogwarts world would contrast and interact interestingly with Louise's magic from 'zero no tsukaima'. Another good character could be Naruto. His determination and unique ninja skills would add a different dynamic to the story when combined with Saito's swordsmanship.
Slenderman would be an obvious choice. He has a connection to Jeff in the horror lore. Their interaction could range from being allies in a shared goal, like spreading fear, to being enemies as they compete for territory or influence in the horror world.
In a crossover with the Avengers, characters like Iron Man and Captain America would be great. Iron Man could be intrigued by the technology of the lightsabers and try to replicate it. Captain America, on the other hand, could admire the Jedi's code of honor and fight alongside them against a common enemy, perhaps Thanos who is also after some powerful Force - like artifacts.
One character that would be interesting to include is Batman. His combat skills, detective abilities, and vast array of gadgets would make him a formidable ally against the zombies. Then there's Katniss Everdeen from 'The Hunger Games'. Her archery skills and survival instincts would be very handy. Additionally, Doctor Strange could be a great addition. His magic could be used to create barriers against the zombies or to teleport the characters out of dangerous situations in the 'highschool of the dead' setting.
Well, if you cross it with the Star Wars universe, Darth Vader could be an interesting addition. His dark power and combat skills would be a great contrast to the characters from Into the Badlands. It would be fascinating to see how they interact and whether they could form an alliance or end up as enemies.