Karthus ultimate and spell effects

Greetings, everyone.

Since preseason I detest Karthus. With Dark Harvest changes Karthus has found a keystone to target specifically low hp targets with higher damage than a patch before and it took quite some time to get used to it. Before this Karthus had no dedicated keystone - Comet and Aery follow the logic of Luden's Echo, hitting the first target alive in the team list.

This leads to champion pick order directly affecting gameplay, making Karthus with certain runes and items stronger if the first target is a squishy and weaker if it's not. Something completely out of anyone's control.

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I propose giving Karthus a way to mark the target(The Kindred way) receiving spell effects with certain cooldown on swap. It would make the champion more diverse in his options, more consistent in his gameplay and easier to balance with numbers changes, removing the randomness.