2 new things for tanks/engagers.

The first would probably be one of the new Runes or a Mastery ability. In either case, it would be for the tanky trees only to prevent cross class abuse.

#Thing 1 Upon inflicting a stun, snare/root/bind/whatever, suppress, airborne, entangle (Amumu's ultimate), or suspension** onto an enemy, the enemy champion will be additionally inflicted with Grievous Wounds for X seconds (maybe the GW will only be applied AFTER the CC ends, I dunno). (Potential cooldown?) If multiple champions are all simultaneously afflicted by the crowd control, then.… (I don't know, either first or all of them depending?)

This is meant to be a tank's counter to draintank champions who can typically survive long enough to come back even once they are CC'd. This would be in the tank mastery tree or rune path or whatever and not an item to prevent people like Yasuo for example from abusing it, or other damage focused champions with hard CCs. ** Supposed to be all the hard CCs I could find that prevent movement at all. Fear/Charm/Taunt stop movement of their own control but still moves them and most tanks don't have them so I didn't include them. Most tanks or engage champions would have a stun, snare/root/bind/whatever, suppress, knockup (like Naut ult) or other such hard CC. Hence the list.

This one could be an item due to the way it works, since it'd have to be an active, and the effect in itself would probably prevent abuse.

#Thing 2 ACTIVE: Target 1 enemy champion. For the next X seconds, neither you nor that enemy champion will be able to deal any damage to each other. However, both you and the enemy champion will take Y times increased damage from all other sources for that duration. After X seconds, both you and the enemy champion will be unable to cast abilities, use Summoner Spells, or item actives for the next Z seconds. (Not a silence. -> stops QSS from being able to get rid of it)

Tanks don't need to worry about damage, and by being able to target a key carry, they would be able to absorb the amplified damage from the other champions while CC locking down the target they chose so that their team could kill them instead.

I see this item being a lot more problematic, but I thought it was interesting, although I'm not sure what the best way to balance it could be.