Flavor and tone aside, there are strong mechanics in Duskmourn with manifest dread, survival, and rooms
Obviously exiling instead of sacrificing is a big deal, but Sothera requires everyone to have creatures in play for it to stick around
Sheldon Menery, the godfather of Commander and head of the RC, even said that the card is too generically good and pleaded with Wizards to Please never print this card (Wizards apparently asks the RC for input during card design)
For six mana you get a 6/6 body with three strong keywords, but the ability here is where things get really juicy
But folks, this is Commander where ramp is everywhere
Either way, in its time, it was a powerhouse Pokmon like no other