There is a video that lists all those skins you're talking about.
Check it here
Please note that these are just visual "buffs" (Notice the quotation marks in the word buffs).
First A few things to note (Disclaimers):
- The video only references skins that you could buy at the time of the making of the video. (about 3 January 2013);
- The "buffs" that these skins give you are very small;
- The Poster references that he may have missed one skin or two;
There are Skins that make your champion appear smaller
- These skins do NOT change the actual hitbox of the champion.
- These skins DO make your champion look smaller.
You will get hit by less skillshots because you are a smaller target and therefore harder to aim at. Basically since it doesn't change your actual hitbox it appears that you are smaller changing the way opponents aim at you. That can help you dodge some critical skillshots.
The skins that make you smaller are as follows:
- Oktoberfest Gragas;
- Hired-Gun Graves;
- Prestigious LeBlanc;
- Totemic Maokai;
- Nunu Bot;
- Battlebunny Riven;
- Spetacular Sivir;
- Highland Tryndamere;
- Tango Twisted Fate;
- Heartseeker Vayne;
- Marquis Vladimir;
- Vandal Vladimir;
There are Skins that make your champions' Skill's Animation Bigger
- Again, these do NOT change the actual hitbox of the abilities, only their appearance.
People try to dodge skillshots based on their animations. Since they can't see the actual hitboxes. So it will be harder for them to dodge the skillshot.
And as you know just one skillshot can be game changing.
The skins are as follows:
- BoomBoom Blitzcrank (the boxing glove is obviously bigger);
- Pulsefire Ezreal (Q is bigger);
- Fisherman Fizz (Lobster Ult);
- Eternum Nocturne (Q bigger);
- Pool Party Ziggs (Q is a baloon and it bounces in a weird manner);
There are Skins that reduce Counter-Play Mechanics
- These skins change something about your champion that can hinder the opponents ability to counter play you, and thus can have a somewhat decent effect on gameplay.
- There is only one skin that the video mentions;
The skin is:
- Frostfire Annie : the stun is really hard to see, especially with the shield on. So you can easily get the unexpected drop on your opponents if they are not watching closely. The stun is also really hard to see even inside bushes.
But I have to intervene and add another to this list. The skin that I personally add is iBlitzcrank. This skin blitz doesn't have arms. So when he hooks, specially from a bush, you can only see the hand come at you and usually when you do it's already too late.
This video is really good and explains why these skins make it feel like a different experience and why they affect some peoples gameplay. I highly recommend you watch it since you asked the question.
- Underworld Twisted Fate in ARAM (The cards are really hard to see);