These colors are often associated with control, artifice, and intricate plans, fitting the intellectual and often politically charged adventures of the Scions of the Seventh Dawn
Mana ramp is a vital component of successful Commander Deck construction, enabling you to accelerate your mana production and cast powerful spells ahead of schedule
Fell the Mighty doesn't target any of those creatures, so a creature with hexproof or protection from white will be destroyed if its power is high enough
So to recap: In the Alchemy format, Dungeon Descent no longer entered the battlefield tapped, cost three less mana to activate, and was still a bad card
This would even do a good deal to tame a Creeperhulk
Right now in Standard I think that makes the card iffy for multicolor decks, but Dread Fugue is right at home in Mono-Black Midrange where casting it Turn 1 is basically free