One of her projects after the Labs 2.0 in the region of Halogen in the Dacutter Island Underworld is built. Rihanna Vicoul uses plasma energy as a high-yield compact battery to make some highly unusual weaponry that not even the Bat Federates often consider.
The Shrink Ray, when it hits an object, encompasses it in an energy field and gradually reduces it's size at a somewhat fast rate. It doesn't last forever, her rule of thumb is that the bigger the object's original size, the sooner it will unshrink. Being able to shrink something in it's entirety is one of it's safety features, as Rihanna has successfully predicted the disastrous results of her prototypes before the final product was completed. Her assistant coworkers could certainly tell you horror stories of the prototype shrink rays at first turning chairs into indiscriminate composite beads of it's original matter, or acting as an inefficient cutting laser or not keeping the target's proportions together, making them unsuitable for use on biological targets, and that one time she almost broke the schwarzchild radius by almost decreasing the matter density of a simple plastic sphere so small that it could make a miniature black hole and suck the surrounding space inwards. Needless to say, it's a dangerous science.
It's well worth it however. Rihanna loves to use this to weaken enemies with, making them easier to defeat or capture with a simple slap, stomp, or to cup them into a glass jar. One of her safety features is that the energy field lasts as long as the shrunken subject remains inside of a space smaller than it's original size, so that they don't get smashed inside of a sturdy container or burst out of the inside of something made of weaker materials.

It's not what Melancho always needs to get into his mini-form but it is how he came up with the idea to have one in the first place after Rihanna shot him with the ray for five seconds. Perhaps that form will be detailed later, but suffice it to say, it benefits his desires to use compactness in ways that Rihanna doesn't anticipate being useful but works out well.

She would work on a growth ray, but it's easier to make things smaller rather than bigger. She can only ignore thermodynamics and the square cube law for so long before it causes more catastrophic failures. It's a job better left to alchemy and magic, but don't remind her that Magic exists on the Shattered Islands or she'll obsess over another plan to capture an observable chemical or elemental state. And by elemental, she means on the Periodic Table, rather than the classical elements of nature.