Murderous Redcap for instance can ping your opponents to death, while Puppeteer Clique can empty their graveyards, temporarily giving you all their creatures, and activating Celes' ability at the same time
Its an army in a can thats perfect for picking up speed, and it can even add a ton of mana in long games
Ramp Much like card advantage in the command zone can be very powerful, ramp in the zone can be equally strong
Archon of Absolution 3W Creature Archon 3/2 Flying Protection from white (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything white.) Creatures can't attack you or a planeswalker you control unless their controller pays 1 for each of those creatures
One legendary elephant creature has now become a planeswalker card
Generally speaking, though, I don't think that any one is more important than the other two