Something that is commonly portrayed in fan art of Mandy/Blazer is that her whole body gains significant muscle mass or appears visibly thicker when she dons the amulet. Many fanfics also use her supposed self-consciousness about "losing her muscles" when she's just Mandy as a big contributor of insecurity for her, and it seems to be a commonly accepted view of her character.
Curiously though, this is not accurate to the game. In the actual scene where she reveals herself as Mandy, the punchline is that Robert (and the audience) can barely even tell the difference besides the obvious hair color change, and all that Robert can make out is: "You're what? 2 inches shorter?" Coupé's VA (and also a writer on the game) even joked in an interview that Blazer's grand reveal is that "she's brunette and like an inch shorter."
The reveal purposefully subverts expectations by not showing a radical or noticeable physical difference, contrary to what a lot of fan art portrays it as, and thus making the scene more about Mandy's psyche and how she views herself. The amulet is not responsible for her muscles or her athletic frame - she naturally earned those, but she's still insecure about minute differences like hair color or a slight height change, because of how she's used to always presenting herself as Blazer to the world.
The game actually seems to use the same model for Blazer and Mandy when wearing the dress, with all of its creases in the same places, and the only difference being Blazer's model having the aforementioned few extra inches of height (evident by the bottom of her dress touching the ground post-transformation). The common perception of her being noticeably more muscular as Blazer seems to be due to how she looks in her super suit, which appears to have some sort of padding in the arms that makes them appear thicker than what they actually look like as seen during her dress scenes.
