Random Design Idea: Ability/ult that works based off enemy mobility

Essentially the way it would work is that if an enemy champion dashes/blinks near you, you gain "stacks" on this ability based on/equal to the distance they traveled (wide radius for this). Casting the ability consumes the charges. It would have a slow built-in recharge system for games where no mobility exists on the enemy team save for Flashes.

Ultimate Concept:

Assuming x champion has 0 Energy Regen to begin with

Ultimate Active: Something something dashes (and maybe does other things) Ultimate Passive: Whenever an enemy champion dashes or blinks near you, gain 15% of the distance they traveled as Energy. Grants 3/4/5 Energy Regen per second. Cost: 400 Energy Effective Cooldown via natural Energy Regen: 133/100/80 seconds

Effective CDR per 400 range dash (Flash max range): 15% or 20/15/12 seconds

Seems like a cool concept to me. Doesn't have to be an ultimate and could even just not be mobility at all and just be any other kind of skill that works based off this anti-mobility charge system concept. Could even be an item or rune effect of any kind (defensive/offensive/utiltiy/etc.).

Item Passive Concepts:

Defensive Passive: When an enemy champion dashes or blinks near you, gain x armor and mr.

Offensive Passive: When an enemy champion dashes or blinks near you, gain x bonus attack speed.

Utility Passive: When an enemy champion dashes or blinks near you, gain flat bonus movement speed equal to 10% of the distance they traveled (max 60-ish)

It's basically like a Energize effect that charges based on enemy movement rather than your own.

I personally think this concept sounds best for an immobile champion to have. Something in the vein of how Poppy is anti-mobility (though she's fairly mobile herself).