I don't know why, but I just can't play some champions without a specific skin.
Some champs I can't play without a skin are :
Sona - DJ Lux - Elementalist Gnar - Snow Day Lulu - Winter Wonder/Dragon Trainer/Pool Party Udyr - Definitely Not Udyr Bard - Snow Day
: All of them; I don't own Major though. 
: All of them; I don't own Toy Soldier though.
: Elementalist.
Dragonwing and Arcade.
: Groovy.
: All of them; I don't own Winter Wonder though.
: DJ and Guqin.
: Pulsefire.
: All of them; I don't own Slayer though.
: Forecast, Frost Queen, and Star Guardian.
: Debonair.
: Officer.
: Candy King.
Brolaf
Ravelord
Lumberjack
Trundle and Karma. If they aren't traditional, they're crap.
I would say Sona, with Muse, but they butchered the already mediocre (but still nice to look at) original splash art, and updated it to be just plain unpleasant to look at with no ethereal Demi-goddess feel to it.
I've considered asking for a refund on the skin (think it was my 2nd or 3rd purchased) after every game I play her.
Also, anything Kat DeSousa did the art for I prefer to skin. She's a talented artist and I want to like the Splashes, but she always makes glaringly subtle fuck-ups that ruin the composition for me. An unnatural and ridiculous over-rotation of an arm, the 4 inch stilettos cropped out of frame of a super tank, a weird, unnatural giraffe neck, an arm that is disjointed and holding an item in a way that should not be possible. It's like every piece of art she's done that made it into LoL, at first glance, looks pretty good, but then you see "it" and you can never unsee it ever again.
Cant play Udyr without Spirit Guard skin. It just doesnt feel same way.
I can't play 
without star guardian skin.
Veigar final boss
sorry but this is kinda irrelevant because everyone is fucking complaining about the clash bug
Kayle. Aetherwing is basically pay to win in my eyes lol. The animations are so much smoother.
