Well, one spell he might create is 'Ice - Levitate'. This spell would allow him to levitate ice - made objects or even frozen enemies. Also, a spell called 'Arctic - Blast' could be developed. It would send out a powerful blast of ice and cold air that could knock back multiple enemies at once. He could also come up with a 'Cryo - Vision' spell, which gives him the ability to see through ice or in icy conditions more clearly than normal, useful for finding hidden things in ice caves or frozen lakes around Hogwarts.
There could be a spell named 'Silk - Shield'. Harry, with his spider - like abilities, might come up with a spell that creates a shield made of magical silk. The silk could be as strong as the real webs spiders make, but also have magical properties. For example, it could be enchanted to absorb dark magic. Additionally, a 'Spider - Grip' spell could be developed. This spell would give the caster the ability to hold onto things as tightly as a spider holds onto its prey or its web, which would be useful in many dangerous situations.
Maybe a 'Fire Illusion' spell. Using her fire powers, she could create illusions made of fire. This could be used to distract enemies or create false paths in a maze - like situation. For example, in the Triwizard Tournament maze, she could have used this to mislead the other competitors.
Harry having ice powers would make the story quite different. In the wizarding world, most magic is more general in nature. Having ice powers would be a very unique and specialized form of magic. He could potentially use his ice powers to explore areas that are normally too dangerous due to extreme heat or fire - based magic. For instance, he could freeze the dragon in the Triwizard Tournament long enough to get the golden egg. His ice powers could also be a key factor in his relationship with Hermione and Ron. Hermione would be eager to research about this new type of magic, while Ron might be both amazed and a little jealous at first. This would add a new layer of complexity to their friendship.
Harry might gain the ability to dodge attacks more easily. Sans has a certain 'instinct' for avoiding harm, and if Harry had this, it would be much harder for his enemies to land a hit on him. This would be really useful in duels, especially against powerful dark wizards. It could also make his Quidditch playing even more amazing as he could dodge bludgers effortlessly.
One spell Harry could create is a 'Lumos Maximus Amplificatus' which would create an extremely bright and long - lasting light, much stronger than the regular Lumos spell. This could be useful in very dark and dangerous places like the Forbidden Forest at night.
He could create an Ice Clone Jutsu, similar to his Shadow Clone Jutsu but made of ice. These clones could be used for various purposes, like distracting enemies or freezing them on contact.
He could create a magical weapon, like a sword with special enchantments. Maybe it could be a sword that can cut through any dark magic shield.
One new ability could be ice - skating at super - speeds. He could glide across water or land, using his ice - skates made of pure ice, and quickly reach his destination or dodge attacks. It would be like a combination of his natural athleticism and his new ice powers.
Another ability could be dark energy projection. Naruto could project bolts of dark energy from his hands or body. This energy could be used to blast away enemies or even to corrupt other things it touches, like sealing jutsu or barriers. It would be a very different and more sinister form of attack compared to his normal Rasengan.
Well, Naruto could gain the ability to heal in a more advanced way. Just as the avatar can sometimes use their connection to the elements to heal, Naruto might be able to do the same with his chakra. He could also have the power to merge with the natural world around him, similar to how the avatar can connect with nature. This would give him an edge in stealth and surprise attacks. Plus, he could develop a new form of sensing, being able to detect not just chakra but also the energy of the elements around him.