The following examples don't seem to fit the trope description of people shapeshifting to forms "dictated by their environment, or the people around them":
All Jokers have a form of empathic shapeshifting, except it's one-shot only (during initial infection), self-imposed, unconscious and uncontrollable, and ends in permanent Shapeshifter Mode Lock. According to Dr. Tachyon, the Wild Card Virus takes a random— or maybe not so random— image from the subconscious, and amplifies it to telekinetically influence how the virus is rebuilding the body. This explains why some jokers have animal or mythological forms, and why some Aces have overly specific powers.
Most mutants actually change their appearance (involuntarily and unconsciously) to match their ideal self-image. Again, usually comes with Shapeshifter Mode Lock.
Similarly, shapeshifting to forms that are "self-imposed" or matching their "ideal self-image" seems to be missing the required external influence from the environment and/or other people.
I've removed these examples for now. If you know of additional context that makes these valid examples, please add them back with the additional information.
The following examples don't seem to fit the trope description of people shapeshifting to forms "dictated by their environment, or the people around them":
This sounds like shapeshifting based on the shapeshifter's own emotional state, not anything external.
Similarly, shapeshifting to forms that are "self-imposed" or matching their "ideal self-image" seems to be missing the required external influence from the environment and/or other people.
I've removed these examples for now. If you know of additional context that makes these valid examples, please add them back with the additional information.
Edited by NotOnAnyFlatbread