I'm about to get akumatized because I have to write this reply all over.

There are two routes I could take, meta and imaginative, so I will take them both

Meta

Recuitment Speech: "Life is unjust and no one wants to listen to you. From now on you, Nangbaby, will have the ability to channel your outrage into strength, and all will listen to what you have to say. In exchange, you must bring me the miraculouses of Ladybug and Cat Noir."

Appearance and Powers: Adult-sized baby with a bonnet, booties, a diaper, and a bib. Wields a rattle which doubles as a megaphone. Screeches and wails are used as sonic attacks, while her rants can annoy people into submission. Those who are subjected too long to her whining will become her minions.

Lucky Charm: A pacifier, of course.

Imaginative

Recruitment Speech: Nangbaby, I am Hawk moth. Since you are tired of those who are stronger than you, I will give you the ability to feed off their strength and make it your own. In return, I ask that you retrieve Ladybug and Cat Noir's miraculouses."

Appearance and Powers: Vampire themed villainess ("Noire" + fangbaby), clad in black and complete with fangs. Due to TV broadcast standards, Nangbaby would only drain life energy via touch, so no blood, no biting. Gets stronger the more she draind. Can also teleport via the shadows and hypnotize. Does NOT have shapeshifting, super speed, invulnerabilty, telekinesis, flight, or any of the other Hollywood/legendary powers.

Lucky Charm: Disco Ball. With this and Ladybug's plan, the heroes scatter the the light which makes shadows dynamic, ruining the teleporting ability and grounding Nangbaby into a single location, allowing them to grab and destroy the object the akuma is hiding in.