Most of the time you counter someones spell, youre countering something they played on their turn, likely to try to win
Monster Manual costs four mana up front, but you then can pay two mana and tap it to put any Creature from your hand into play
First and most important was Gravecrawler, a card that is normally worse than Bloodghast (although very similar as a 2/1 that can't block) but a major upgrade with Vengevine because instead of returning for free, you cast it from the graveyard for a single mana (assuming you control a Zombie)
It is like momentum and velocity in physics, one is a property of the other but they are not the same thing
Why you cant sacrifice a creature at any time in MTG Sacrificing is a game action that only happens when something tells you to do it
Ghired does a little bit of everything, and I think he has enough tricks to make him both an interesting build-around commander and a very powerful aggressor