Discard only works from your hand
Normally in Limited your opportunity to take a Constructed power-level card may only come around once or twice per draft, but in a Cube draft this opportunity presents itself pretty much every time you look at a card
My Grixis Cube is about leaning in on what high-powered Cubes already do well, whereas Autumns Bant Cube is more about exploring a wider range of unique archetypes
Rakdos Tree 4 Bloodtithe Harvester 4 Agatha's Soul Cauldron 4 Blackcleave Cliffs 4 Blightstep Pathway 4 Blood Crypt 4 Fable of the Mirror-Breaker 4 Fatal Push 4 Tree of Perdition 4 Voldaren Epicure 4 Voldaren Thrillseeker 4 Thoughtseize 3 Inti, Seneschal of the Sun 3 Mutavault 3 Raucous Theater 2 Swamp 2 Flamecache Gecko 1 Takenuma, Abandoned Mire 1 Mountain 1 Castle Locthwain 3 Path of Peril 3 Leyline of the Void 2 Duress 2 Laughing Jasper Flint 2 Ob Nixilis, the Adversary 2 Alpine Moon 1 Jegantha, the Wellspring Rakdos Tree shows that Sorin, Imperious Bloodlord plus Vein Ripper was not the only combo available for a black-red midrange deck
Other creatures will get the benefits (or, occasionally, drawbacks) of those things, but other creatures don't have counters or stickers on them unless they actually do
So the remainder of the spells in the deck are focused on not only recycling cards but also keeping your threats alive
