Plenty of playable black spells also happen to throw a few cards from your deck into the graveyard as a bonus, and mechanics like delve, dredge, escape, undergrowth and unearth all reward you for it
If some of the creatures are illegal targets as Undercity Upheaval tries to resolve, the original distribution of counters still applies and the counters that would have been put on the illegal targets are lost
Any card that puts -1/-1 counters on something, or itself, can be a potential source of card drawing
A formidable Cube staple to supercharge mono-red decks, Im most intrigued by this red planeswalkers -2
Note the creature types for those types too
If you go off on turn 3, which is the goal for most cascade/suspend decks, thats a tough board for your opponent