Make Grasp of the Undying Great Again

This is a very quick rune idea that I'm sure Riot have looked into but this post is just in case they haven't. Next para is my TL;DR.

Grasp of the Undying to activate after a champion falls below 25% health. After two seconds, the next single instance of damage within 2 seconds heals for 50% of the damage dealt. 45s Cooldown. Only works against champions.

The idea is that tanks don't have high power abilities that deal all of their damage in one go or if do, they have another window to focus on (Darius' ult, Garen's ult, Illaoi's ult). This rune gives tanks a bit of survivability and lets enemies prepare in 2s for a veey important ability coming their way. On carries, it rewards those who don't turn away. A Vayne can turn up Silver Scrapes and Tumble back into a fight, but 25% of Vayne's HP isn't much to live on.

The current GotU is purely a name for a tank rune. I've been listening to Pentakill recently and thought about how underwhelming this rune was for such an amazing name. I was also inspired by my many hours playjng Sion and how awful post death passives are. So I thought to make it pre-death and suit its name.

Obviously I am not a Rioter and I have no clue about how to balance, but I think this rune can be balanced very easily. 25% could be altered for ranged characters The cooldown can be changed The heal amount can be changed A base heal could be added The window can be changed The delay can be changed The lifesteal could scale The cooldown could scale

The problems that may arise with this rune is the simple idea in a game where every character is a niche and is a single case.

Possible Problems: Cho'Gath - 25% of his HP is enough to survive 2 seconds on in so many cases. 50% of his Feast is too much damage. Damage healed should not be true damage: will also remove Darius and Garen vs Villain. Tryndamere - Toxic to play against since he can, without a doubt, survive on below 25% of his hp for 2s. Damage could be decreased for crits since the randomness is somewhat unfair anyway. Vayne - RQ for 1s in stealth. Q crit does insane damage.

Imo I think lifesteal should be removed on the attack since this ia pretty much 50% extra

Thanks for reading this, remember to upvote if you like it and comment below with feedback or some ideas for abusing champions. :^)