"In that room, my mother came to me. But it was not her. It was something else."
"Ah. My son, I suspect. We can take many forms. The shapes we embody are merely a reflection of the life force around us."
― Anakin Skywalker and The Father (Star Wars: The Clone Wars)
"Above-All-Others is both male and female?"
"So our senses perceive it moment to moment."
"Annoying, is it not?"
"No, truly wondrous"
― Adam Warlock and Thanos after meeting the One-Above-All (Marvel Comics)
The ability to have an appearance that differs to those that look at them.
Eyes of the Beholder
Subjective Appearance Shift
The user's appearance differs depending on who sees them, on what the user would look like according to seers tastes and/or experiences. The perceived appearance varies from person to person and can include changes in race, voice, and mannerisms to present anything from an ideal figurehead to someone most hated by a viewer.
Yuuko Kanoe (Tasogare Otome × Amnesia); limited to appearing as one's greater fear
Chandra (Top Cow); limited to appearing as one's description of the most beautiful women
High Succubus (Valkyrie Crusade)
Cynosure/The Meeting Hall (Forgotten Realms)
Being personifications, the Seven Endless (DC Comics/Vertigo) all look different depending on those who see them depending on their species, culture, etc.
The Weird Sisters (Gargoyles) are able to disguise themselves, their disguised appearances differing to those that see them...
...looking like a group of schoolgirls to Goliath...
...and a group of elderly gargoyles to Demona simultaneously.
Xion's (Kingdom Hearts) appearance varies depending on who perceives her, with Roxas and Axel seeing her as a black-haired girl...
...and Xigbar seeing her as Ventus.
Shirohime (Lance N' Masques) appears to be a normal horse most of the time, though others will sometimes see her as a normal human girl, a horse-girl, a child, or even a horse with some human-like features.
Gaea (Marvel Comics) has been known by many names throughout Earth's history, and can appear in the form of whatever image she was worshiped as by any race on Earth, even multiple ones simultaneously.
Honest John (Marvel Comics) is able to appear to others in the form of what appeals to their individual tastes of what they consider a great leader.
Dani Moonstar/Mirage (Marvel Comics) learned to throw up illusions around herself to appear as whomever those who saw her found most suitable to their eyes.
Though often depicted as Caucasian in appearance, Santa Claus (Marvel Comics) actually appears to most people in their own racial features, though he usually retains his iconic white hair and beard.
Everyone who sees Izanami (Noragami) sees her in the likeness of the person they feel most comfortable with...
...appearing as Hiyori Iki to Yato, for example.
Aphrodite (Percy Jackson series) appearance would change to appeal to each person who gazed upon her.