HER POWER: GHOSTLINESS (she's not a ghost herself, but has the features and abilities of one)

first things first, you might notice her lack of...legs, I'll get into that soon

Janna is a very unique and tragic character in the show, she starts out like any other ultimatum for most of season 1, still pranking people like her original show self

however, in the season 1 finale, she and the witness have an altercation that results in her doing something to screw up the witnesses' plans, the witness attacks her in an outrage, later in the episode, Star and Marco later break into his lair/base/hideout/whatever and find her brutalized, covered in blood, crying, only covered by debris, and her legs are completely gone

Star and Marco try to carry her out of there, but they get confronted by an enraged Witness, throughout the entire battle against him, Janna is terrified

after it's all over, they bring her to the hospital, and find out something shocking, wedged inside her are two metal things

basically, the witness brought those metal things from the future he came from to use on toffee, their effect is halting the users power gain ENTIRELY (they can't get any stronger while the metal things are there) as well as preventing the regeneration of lost limbs, however, the witness used his only two on Janna instead since his plan was foiled, and now SHE has to deal with the effects

now she has to watch as everyone around her becomes significantly stronger than her...and it's going to stay that way for a very long time for her

she has to deal with PTSD from the witness's attack as well, and boy oh boy does it sting A LOT for her

throughout seasons 2 to 5, she is mostly confined to a wheelchair, her parent's cycle through caretakers for her (one of which being Tom), if she isn't in her wheelchair, she is crawling around, she is generally okay, though due to her severe insecurity about being weaker than literally every other ultimatum, she is prone to emotional outbursts, and she has to be extra careful around others as they could thoroughly eviscerate her

however, at the end of season 5, after a high moment, she receives awful news, due to complications, Tom can no longer be her caretaker

this is awful, she is going to be torn from her favorite caretaker, and now she's going to have to deal with changing to another one, one who likely won't understand her as much

she can't handle it, she crawls off away, crying...but then she sees him

Toffee.

in the rain, he offers her a deal, he needs something from her (uncertain for now), and since the metal things in her are linked to him, he can remove them, and she will finally get her legs back and get stronger

she has heard bad things about Toffee, VERY bad things...but she isn't thinking straight, she's desperate...he's desperate as well

So she accepts.

(copy and paste from the tumblr post)