Last game I played against a karthus (using revive and teleport spells). He rushed a mejai and around minute 30 i started noticing he had more charges he should have (he died plenty of times and didnt kill as much as to have mejai on 15 stacks).

I started checking out his stack, when the fight started, the kills he made during the fight, the time of his death and the number of kills made during his passive. The math showed something wasnt right. Maybe it's a glitch with his passive, maybe with revive. Still worth it to check it out

thx Riot for a work well done.