In case of Morde rework, a little suggestion...

I don't play Morde and am not hardcore fan of his so this suggestion is purely opinion based on what his theme seems to me and may very well not be much approved by vision of Morde's mains, so this is just to throw my two cents into things, nothing much serious.

So how about we turn Morde into the King of the Wild Hunt (The Emperor of the Death Hunt)? The whole theme of spectres being his army, him once ruling over entire Runeterra plus Harrowing allowing him to ride in the skies plus the legend has significant germanic roots with German folklorist being the one to define and name it while Mordekaiser basically is German for The Emperor of Murder - doesn't seem so unfitting to me.

Hecarim, though removing part of his uniqueness, might be one of a kind, of entire army of spectral soldiers, half-man, half-horses, forming the Wild Hunt, following their King, with Hecarim being their general and right hand of Mordekaiser.

Since the legend has also strong Nordic roots, how about connect it to the lore of the Watchers? Maybe make Mordekaiser Watcher himself - since alongside the King being random spectre or historic/legendary hero, the King was mainly one of Woden's/Odin's interpretations.

I'd go so far as to make Mordekaiser be "Loki" in the Watcher lore and implement Jörmungandr (Nagakebourous?), Fenris and Hel (Lissandra) as his kids somehow. He'd be banished from the Watcher world for some crime and thus his conquering in the world would begin.

Summa sumarum: Making him originate from the Watchers (explaining why he could achieve what he achieved even prior to resurection after Ruined King's ritual) and be The King of the Harrowing-like Wild Hunt.