Masquerade

Masquerade is a maroon pegasus. She has a short, brown mane with pink highlights that falls to the right side of her face. She has green eyes and a cutie mark of a masquerade mask on her flank. As she is a pegasus, she has wings on her back; they’re decently expansive when splayed. Her height is normally a mere 5'2", and her build is lithe but toned, like that of a gymnast.
Masquerade possesses a very powerful amulet that allows her to transfer size to or from others with a touch. It also allows her to control her internal hammerspace, adjusting her apparent size as needed. Excessive use of this artifact caused her to be the most physically strong being on the planet prior to the events of The Call of the Forgotten. It also grants her a few other abilities, listed below.
Masquerade grew up around Baltimore. From a young age, she was fascinated with the prospect of acting. To be someone else, to hide one’s own thoughts and feelings. Her mother supported her desires and gave her ample opportunities to watch plays and also practice her technique. Her father helped her to develop the discipline she needed to succeed. She went to the state university, then started acting in plays after getting her bachelor’s degree. She acted for a few years, always wanting to make it big, but never succeeded, staying small-time. She was successful, but not overly so.
That all changed on one fateful night. After the final showing of one of her plays, the mare decided to treat herself. She went to an ordinary jeweler’s shop, and saw a sapphire pendant that caught her eye. She tried it on, and something immediately clicked that she had to have it. She purchased it from the store and went home; the store later found that they had no record for where they acquired such an object. It’s likely that it was from some other dimension.
Over the next few weeks, Masquerade’s mind and body slowly shifted. She retained her full memory and abilities, but slowly shifted from kind and caring to one consumed by greed. The amulet also made her a bit stronger and caused her to slowly grow a shaft. Over the course of the next few years, she slowly discovered her powers, and used them to climb higher and higher in power. She’s tangled with all sorts of powerful beings, ultimately usurping them all and gaining most of their strength as well.
The next few years of Masquerade's life were a period of indulgence and hedonism. She stole what she could from people, then eventually moved on to dragons, taking their size and wealth for her own. She was in an extended, nonexclusive relationship with another member of the top tier, Aiko Ai, and amassed a fortune worth hundreds of millions of dollars. She was living near Seattle at this time, in her own mansion that she had constructed.
Things started to change with The Call of the Forgotten, however. Masquerade spent most of October 2020 in the West Pacific, taking on the rampant Kaiju attacks and adding to her own mass. Over the course of a month, where she was averaging over two targets a day, she gained enough mass so that, uncompressed, she stood a full 1500 feet tall with a well-muscled stature.
Given that she was already past the point of physicality mattering at the end of Call, she was once again approached by Tragedy and Comedy. They offered her a deal: In exchange for most of the size she'd stored, they would remove some of the limitations of the amulet, grant her some magic resistance, and, most importantly, return her to the kind mental state she had prior to putting on the amulet. Figuring that the size could be regained, she eagerly accepted, but immediately felt guilt about using her powers at all and the mass of sorrow that was in her wake. She now tries to rectify her past through current and future deeds.
Here's a full list of abilities granted to Masquerade by her amulet:

• Steal size from other people with physical contact. This includes both full body height and individual parts. She cannot gain a part if she doesn't have it (so she can't sap from a unicorn to get a horn, she can't sap from a lizard to get a full tail, etc.) If she saps general size, other body parts will shrink to match, even if she has no corresponding part (e.g. sapping a unicorn's height won't make their horn become oversized relative to their head.) The drain rate is proportional to the area of contact and distance between the contact and the affected part. This ability also lets her steal physical strength, but does not allow her to steal intelligence. All transfers are in mass, not by length/height. She can use herself as a "conduit" to transfer between two other parties. Her eyes glow as blue as her amulet when using this ability.
• Have hammerspace insides. Her body is quite a bit larger on the inside than it is on the outside; she chooses the scaling factor from anywhere from 1x to 1000x. Various body parts can have independent scaling; she can have a treasure vault in her womb and then swallow someone whole and have them make a normal-sized belly bulge. This also extends to her muscles; she can have a bicep that's effectively over 2 meters thick while still retaining her normal appearance. This gives her incredible strength (and also incredible durability, since people have to work through a surprising amount of flesh to get to the relevant bits.)
• Control her digestion. She has complete control over how fast her guts process something or someone, from never to near-instantly. Ingesting capsaicin will cause her to lose control and force it to go into overdrive, faster with more.
• Store souls. Any prey digested within her won't let their soul "pass on" unless she chooses; the souls are instead stored for future use. This blocks many forms of reformation. She can then burn souls, as described later.
• Break free of mental effects. If she gets mind controlled or otherwise mentally altered, within a second or so, her amulet will revert her mental state to whatever it was before the effect. See here for something quite similar. Her eyes will glow when this happens. If under a sustained effect, this will stay permanently active.
• Burn souls. Masquerade can permanently destroy souls to gain a temporary benefit. These temporary boosts include: strength increase, durability increase, speed increase, hammerspace scaling factor increase, self-revival. All of these are exponential with the number of souls burned and can be adjusted to be more powerful for a shorter burst of power or longer for less power.