@Malicious Metal, I think I've found a direction for a Mordekaiser rework, care to comment?

Mordekaiser is a malicious embodiment of the black mist who was banished out of his one host, the ruined king, by Yorick. Weakened without a host body, he possessed the Ruined King's armor, and wanders Runeterra seeking a worthy host...

New Ult: Mist's Entrance

Mordekaiser Possesses a champion he's recently damaged, leaving behind his armor and taking control of them for up to 7 seconds. Mordekaiser gains access to all of their abilities, items, and has them become an ally for the duration. Their current cooldowns are also applied to Mordekaiser during this time. At the end of the duration, Mordekaiser exits the target and returns to where his armor was left, dealing damage to the target, increased based on how much damage Mordekaiser dealt to enemies while the target was possessed.