If Riot doesn't want Tenacity to apply to Knock-ups can we at least have an alternative to choose?
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##Diver's Boots
- Cost: 1100 Gold
- Recipe: Boots of Mobility + Ruby Crystal + 400 Gold
- 250 Health
- UNIQUE Passive - Enhanced Movement: +35 Movement Speed
- UNIQUE Passive: Grants Heavy if you have at least 2000 maximum Health.
Heavy: Reduces they duration of enemy knock-ups effects to at most 0.5 seconds when above 80% maximum Health, and at most 0.75 seconds when above 60% maximum Health. Reduces the effectiveness of enemy knock-back effects by 20%.
I think this would be more interesting than just adding a new stat "+25% Heavy" to the game. This version is more dynamic and has more flavor. It also keeps champions with knock-up effects' early game strength intact because you need 2000 Health first, that way it shouldn't affect balance too much.
You could have the item's picture as a buff and it changes color to show you how 'heavy' you are at the moment similar to Thresh's E.