I can think of ONE way to even out mobility creep, but it involves Items that weakens the owner...

The main idea is, those who need the item will get the item. Those who don't need the item can try to buy it if they want, but they will pay for it.

Riot is going to keep on making champions that makes and weep. They're going to keep making champions that laughs in the face of and his ilk.

They're clearly not going to find a way to make mobile champions pay for their mobility. Therefore the only way I can think of them finding a way to even the scale is..............with items that gives champions a lot of power to champions somehow, BUT come with a negative side effect of specifically nerfing the range of any gap-closing abilities.

For instance, like a powerful tank item that also has Warden Mail's old Passive...but it also nerfs any leaps/blinks/dashes/etc. Therefore anyone can build it, if you're Garen, you can build it and maybe, just MAYBE he'll catch that elusive Vayne now. But if you're Irelia, you will get all the perks Garen just got, however your dashing ability will get a hefty range nerf.

How does that sound for evening the playing field?

edit: I should probably add, that this wouldn't affect Summoner:Flash. And champions such as and will take a HEAVY hit from the item as their gap-closer is also tied in with a skillshot nuke as well. But then that's the idea, those who need it will get it, those who don't need it can still buy it if they thought up a strategy, but they'll pay for it.

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Doesn't do jack about low ranged immobile ADC's, but one problem at a time. Let's start with champions whose immobility overshadows everything else about them.