A full Yuumi skin gallery, plus the practical point: some skins change the silhouette enough to matter in a fight.
Before the cosmetics: Yuumi is a support at 425 attack range whose job is to make somebody else win a lane, then convert map presence into objectives.

Yuumi has 10 skins, excluding chromas. The art below is the in-client splash.
Skins change no numbers. They are not therefore free of consequence — a skin that alters the silhouette or recolours an ability changes how quickly an opponent reads what you just cast.
That cuts both ways, and it is the honest reason some players keep the base skin on champions they take seriously.
Periodically, when Yuumi strikes a champion with an attack or ability, she restores health to herself and the next ally she Attaches to. While Attached, Yuumi generates a special bond with her allies. The ally with the strongest bond enhances Yuumi's abilities while she is Attached to them.
Yuumi fires a missile, dealing damage and slowing first target hit. It deals bonus damage and an enchanced slow if it takes at least 1.35 seconds to get to its target. While on her Best Friend, the slow is always enhanced and grants bonus On-Hit damage to her ally. While Attached, the missile can be controlled with your cursor for a brief period.
Yuumi dashes to a target ally, becoming untargetable from everything except turrets. While on her Best Friend, she gains Heal & Shield Power and grants her Ally On-Hit healing.
Shields Yuumi and boosts Move Speed and Attack Speed. If she's attached, she passes it to her ally instead.
Yuumi channels five waves that damage enemies and heal allies. Yuumi can move, attach, and cast Zoomies! while channeling. While on her Best Friend, this spell also follows her mouse.
A magical cat from Bandle City, Yuumi was once the familiar of a yordle enchantress, Norra. When her master mysteriously disappeared, Yuumi became the Keeper of Norra's sentient Book of Thresholds, traveling through portals in its pages to search for her. Yearning for affection, Yuumi seeks friendly companions to partner with on her journey, protecting them with luminous shields and fierce resolve. While Book strives to keep her on task, Yuumi is often drawn to worldly comforts, such as naps and fish. In the end, however, she always returns to her quest to find her friend.
Skins are tied to the account, not to you. Anything bought on a smurf stays on the smurf — worth knowing before spending real money on one.
Full Yuumi page — abilities, stats and every skin →