Was thinking about this thread this guy select made and came up with some ideas as to how skins could change entire playstyles without being pay to win, just adding more layers of customisation to the game.
To give some examples i'm going to use vel'koz as his skins all portray different types of champs.
Firstly his standard skin will remain exactly the same.
Battlecast vel'koz. The idea here is to make a tank vel'koz that wants to be in the middle of the action applying far less damage but applying that damage more quickly also has more crowd control.
Passive =Changed completely all abilities now do true damage however all abilities now do **half** the original damage. Furthermore all abilities now scale half as much with ability power.
Armour and health +50% at level 18 = from 85 to 127 and magic resist from 39 to 44
Q range decreased by 100 units. Q no longer splits but increases slow duration by 0.5 seconds. cooldown from 7 to 5. Mana cost halved. at all levels.
W range decreased by 50 units. No longer hit's twice but stays on the ground longer and works like singed's W e.g slows heavily. no change to cooldown.
E range decreased by 50 units. cooldown from 16/15/14/13/12 to 14/13/12/11/10
R range decreased by 100 units. slow increased from 20% to 30%.
Explanation. :- Vel'koz is a bit bulkier with less range, and terrible damage and scaling however he can now build very tanky and still output reasonable damage and can perform the tank role for the team, his wavepushing has been somewhat butchered as both W and Q no longer hit as much. But in the middle of teamfights can ignore all resistances and be a general nuisance with more disruption and spamming more abilities.
In my opinion quite balanced i don't think every ability doing true is broken and it will have much less damage than standard vel'koz.
Arclight vel'koz. The idea here is to make vel'koz an actual artillery mage because at the moment although classed as "artillery" he's outclassed in this role by xerath and ziggz and big secret most of vek'koz's damage is applied from upclose. Infact the closer you are to vel'koz the more ticks i can get on the passive quicker therefore apply way more damage.
First change laser range doubled, double mana cost. cooldown from. 120/100/80 to 140/120/100. vel'koz can now move during the laser animation, vel'koz will continue moving to where the last mouse click was pressed before lasering at half the usual movement speed.
Passive true damage removed completely. Vel'koz's abilities now scale with distance travelled (hitting abilities from further away applies bonus damage.
Q range increased +100 for both the initial range and the split, cooldown increased +2 seconds.
W range increased +100, Now works like morganas W and isn't affected by the passive is just a wave clear tool.
E range increased +200, + seconds cooldown. Now this ability can feel like a true bombardment tool from a long way away and yet very dodgeable.
Explanation. Getting numbers right here is going to be difficult and i'm no mathematician. Essentially now his ultimate can be used from much further away as laser doesn't have that amazing range to begin with and it will no longer apply true damage but it can be used in games where there are a lot of back line squishies that don't want to be in the fight champions like ashe and ziggz can hide no longer. Also punishes people that don't build defensive items.
Lastly my idea for "definitely not vel'koz" would be insane.
New passive :- all abilities apply bonus damage to minions.
Q no longer splits but explodes on impact, impact radius large enough to hit 3 minions together like jayce's Q.
W no change.
E Hits everything it passes through like anivias Q.
R now has a 10 second cooldown but is instead like a sniper rifle and shoots in single bursts dealing 100 +10 per level.
Just some ideas. I think this could be pretty cool if balanced well for all the skins in unique ways.