What champions, in your opinion, have "required" skins

I. E. in order to play the champion and feel like a badass, you need the skin.

For me it's dunkmaster darius and spirit guard udyr (these are just two)

Others:

Spooky gangplank

Groovy Zilean

Lollipoppy

Gentleman Cho'Gath

Brolaf (let's be real - a champion who says your mom in their dialogue is automatically op)

What are your favorite/important skins?