Another possibility could be Neville. Neville is often around Harry, and he has his own insecurities and growth arc. If he were to become Harry's hand, it could be a great way to explore Neville's character further. He could gain confidence in this strange new role, and Harry could learn to rely on Neville in a whole new way.
Hermione could also be a likely character. Given how much time she spends with Harry, there are plenty of opportunities for a magical experiment or accident to occur. And with her vast knowledge, having her as a hand could be both a curse and a blessing for Harry. He would have all that knowledge at his fingertips, literally, but also have to deal with Hermione's bossy nature even in hand form.
Perhaps Harry makes Draco his hand. This could lead to a very different dynamic. Draco, now in this odd form, would be forced to rely on Harry. They might start to understand each other better. Harry could use this situation to try and reform Draco, showing him the good in the wizarding world that he has been blind to due to his family's influence. They could work together to solve a mystery in Hogwarts that they couldn't have solved alone.
Neville Longbottom could be a likely candidate. He has shown great courage and has been through a lot. If the situation was dire enough, Harry might train him to be a more effective fighter, bordering on a killer, to protect Hogwarts and the wizarding world.
I think Harry and Blake could also be paired well. Blake's intelligence and her past experiences with the White Fang could be complemented by Harry's knowledge of fighting dark forces. They could bond over their shared experiences of fighting against those who want to bring harm and chaos, whether it's the Grimm in Remnant or Voldemort in the wizarding world.
Definitely Hermione. Her intelligence and vast knowledge of magic would be a great asset if cloned. She could help solve complex magical problems and come up with strategies in battles.
Hermione is a very likely candidate. With her intelligence, she could easily start a business. For example, she might open a library - like establishment but with rare and restricted magical books that she has managed to collect through her research. She could charge a membership fee for witches and wizards to access these valuable resources.
Nymphadora Tonks is also a great candidate. She's a Metamorphmagus, which means she can change her physical form. In hand - to - hand combat in fanfiction, she can use this ability to surprise her opponents. For example, she could suddenly make her limbs longer to reach further or make her body more flexible to dodge attacks more easily.
Hagrid, of course. He loves all kinds of strange and dangerous creatures. He would be the first to be intrigued by the Indominus Rex and would probably try to approach it to see if he could take care of it or at least understand it better.
Probably Harry Potter and Indiana Jones themselves. Harry's knowledge of magic and his experience in fighting dark forces could complement Indiana Jones' skills in exploration and combat outside of the magical realm.
Clawdeen Wolf might be the one. She's confident and brave, just like Harry. She could see Harry as a kindred spirit. Her fashion sense might also intrigue the Hogwarts students. She would probably befriend Harry and then introduce him to the wild and fun world of Monster High, and in return, Harry could show her the secrets of Hogwarts.
Harry Potter himself might be a likely candidate. He has experience in facing life - threatening situations and has a strong sense of justice. His skills with a wand could give him an edge in combat and in finding resources. For instance, he could use the Patronus charm to keep away dangerous creatures in the arena.