No, it's not legal. Impersonating anyone, even a fictional character, can lead to legal consequences if it causes harm or violates the rights of others.
As far as I know, Thunderball didn't impersonate Electro. Comics usually have distinct character arcs and storylines for each character, and this particular situation doesn't seem to be a part of it.
In fanfiction, Loki could also enlist the help of some other characters or magic items to help with the impersonation. Maybe he finds a magical amulet that allows him to not only change his appearance but also adopt the personality traits of the Avenger he's imitating. He could also use his shapeshifting abilities to not just look like the Avenger but also feel like them. For example, if he's impersonating Hulk, he could somehow make himself feel as strong and angry as Hulk, which would make the impersonation more convincing.
The main character of this novel, Li Dan, transmigrated into the body of a Qi Practitioner named Ouyang Wendu. Unexpectedly, he killed a disciple of a sect. In order to avoid being hunted down, he pretended to be a dead disciple and entered the sect, starting his cowardly and unusual path of cultivation. I hope you like this fairy's recommendation. Muah ~😗
An example of a sentence describing a sound is as follows:
The voice seemed to come from a distant valley, and it gradually became clearer.
Hearing her voice, I seemed to hear a breeze blowing past my ears, bringing with it the fresh fragrance of flowers.
3's voice was soft and infectious, and people could not help but be attracted.
Her voice was as clear as flowing water, making people feel relaxed and happy after listening to it.
The voice was so clear and pleasant that people couldn't help but listen after hearing it.
6's voice was loud and powerful, and it sounded very shocking.
7's voice was full of energy, making people feel excited and curious after listening to it.
8's voice had a hint of dullness that made people feel a little depressed after listening to it.
9's voice had a mellow tone that made people feel at ease and comfortable after listening to it.
10's voice was a little hoarse, making people feel a little tired after listening to it.
Here are some sentences describing sounds:
Her voice was as clear and pleasant as the chirping of birds in the morning.
2's voice carried a deep sadness that was irresistible.
The voice contained a powerful force that attracted people involuntarily.
Her voice was as gentle as the spring breeze, making people feel endless warmth.
The voice was as loud as the surging waves, making people feel the passion of life.
His voice was hoarse like an old man's sigh, making people feel the vicissitudes of time.
The melodious sound of the song was like classical music, making people feel the charm of culture.
8's voice was as loud as firecrackers in the night sky, making people feel passion and hope.
Her voice was as sharp as an elf's singing, making people feel the purity of their souls.
10's voice was as gentle as a drizzle, making people feel warm and harmonious.
It could be the Sage of Six Paths. Since Naruto has the power of the Nine - Tails and is on a path to becoming a great ninja, the Sage might be trying to communicate with him through voices, guiding him to fulfill some greater destiny.