She can alter a body's molecular configuration, size, shape and the like, even adding mass or 'accessorizing,' as she calls it, by converting the air molecules surrounding her target along with him or her.  A person changed in this way remains in their transformed state unless Catalyst either reverts them (by rewriting the molecular codes with her powers) or-- for some reason-- if Catalyst's own consciousness is forcibly removed, by KOing, for instance.  It is believed that Catalyst's powers somehow locks the target's original molecular code into their new forms and keeps them from reverting by means of the low-level radiation she constantly emits.  This radiation must somehow be maintained on a subconscious level, because on the occasions that Catalyst has been knocked unconscious, the radiation inexplicably dissipates and her targets have unexpectedly reverted to their normal states.

Unfortunately, this can be used to a heroine's advantage; since Catalyst's mind is human, it can sometimes take time to mentally 'craft' an appropriate molecular bond.  And she has been known to be pushed to irrationality by 'critics' of her chosen transformations.  Besides that, she might be thwarted by particularly difficult substances to mentally envision-- a heroine like Shifter, who can alter their own molecular structure, could prove a very useful ally against her.

Larissa's second mental 'flaw' is her rather sadistic nature.  It does not always surface, but she has a near-sexual affinity for displaying the control and the power she has over a victim.  It would not be above her to torture a victim by transmuting them and allowing their consciousness to remain intact until they are fully transmuted.  She has not yet had occasion to do so, but would likely enjoy psychologically breaking people, forcing them to do things against their will and capturing the moment.  She has not yet completely learned the subtleties of using fear and psychology to her advantage, but she's a quick study.