Android 21 from Dragon Ball fighters is probably the most terrifying creature in the Dragon Ball universe.bBecause similar to cell, she is made from the cells of every z fighter and enemy they have fought. The difference is that she is from the super era... Which means that she is a problem.
Let's list off some powers of the z fighters they haven't used in a while that she has access to, size changing, creating clones, growing multiple arms out of your back, the oozaru transformation, zenkai boosts, the ability to copy techniques after seeing them once, piccolo's ability to just create demons, the clothes beam, the ability to reincarnate into a stronger version of yourself after death, the ability to breathe in space. The ability to fuse with other people and get stronger, the ability to create Dragon balls and a wish granting dragon that you can make the rules for. The kaioken
She has access to, all of frieza's abilities like his telekinesis, his ability to survive in space, his ability to transform in order to make himself weaker, and then most frighteningly, his limitless potential. She also has cells regeneration, his ability to create cell juniors, his ability to absorb people and take their abilities, the Androids infinite energy generators, and then we get to the fun stuff, the Kai's magic, Babidi's magic, the stone spit of Dabura, all of the powers of Buu, shapeshifting, buu's terrifying and accurate eyesight that allowed him to see how many people were left on the planet. Not to mention, everything in super up to the Goku black arc
Not only would her list of abilities and techniques be longer than Santa Claus's naughty list, but a fully realized Android 21 would possibly be the most terrifying threat in Dragon Ball. Realistically speaking, I have no idea why she isn't talked about more or why she is considered a bit of a joke?
Especially when a fully realized version of her, would be literally unstoppable.