I think Deadpool would be a great crossover character with Johnny Gat. They both have a crazy sense of humor and are not afraid to get into some wild and violent situations. Their banter would be hilarious as they fight side by side against bad guys.
Batman could be another interesting crossover. Batman's dark and brooding nature would contrast with Cage's more flamboyant style. They could be forced to team up to solve a mystery that involves some sort of magic or otherworldly elements, which would be new territory for Batman and something Cage is more used to in the Mortal Kombat realm.
A crossover with a fantasy realm could also be cool. Picture Johnny Gat in a world of magic and mythical creatures. He might initially be skeptical of the magic around him but quickly learn to use it to his advantage. He could form an unlikely alliance with a wizard or a warrior elf to defeat an ancient evil that threatens the land.
Superman from the DC universe. Superman stands for truth, justice, and the American way, but his methods are often more lenient compared to Akainu. The two could have a philosophical debate about justice while also having to fight a common enemy.
A character like Dracula could be an interesting crossover. His immortality and dark powers would contrast with Aruto's nature. Also, Merlin from the Arthurian legends would be a great choice. His magic and immortality could lead to some really cool interactions with Aruto.
Definitely Superman. Superman's super strength and Gohan's Saiyan power would make for an interesting combination. They could have a friendly sparring match to test their limits. Another good character could be Ichigo from Bleach. Ichigo's sword - fighting skills combined with Gohan's martial arts and ki blasts would create some epic battle scenes.
Kakashi from Naruto himself could be part of a 'grey' themed crossover within the Naruto universe. Maybe a situation where Kakashi's past and his more mysterious side are explored further, and Naruto has to work with him in a darker, more complex mission that delves into the grey areas of the ninja world.
Definitely Dante from 'Devil May Cry'. Dante is a stylish and powerful demon hunter. His acrobatic combat style and his cocky attitude would contrast well with Death's more stoic and purpose - bound personality. They could end up in a situation where they have to fight a common enemy that threatens both their worlds.
Goku from Dragon Ball Z could be an interesting crossover character. His raw power combined with Sasuke's strategic use of the Rinnegan could make for some amazing battles and interactions. They could learn from each other's fighting styles.
Solid Snake from the Metal Gear series would be a great choice. His stealth skills and military expertise would contrast with Travis Touchdown's more brash and direct fighting style. They could be forced to work together on a mission, and learn from each other's ways of combat.
Alice from Alice in Wonderland could also be an interesting choice. Her curious nature would lead her to explore the world of Young Dracula. And Young Dracula might be both amused and a bit annoyed by her constant questions and her fearless attitude in the face of his vampiric self.