The concept for Golgari Rush is to get creatures out fast and grow them quickly through a combination of Undying and Evolve. Trading creatures isn't a bad thing in this deck. Sacrifice spells and abilities make this deck work even faster. Once the VIPs show up, the graveyard becomes a resource for +1/+1 counters. This allows the creatures to grow to absurd proportions. There are just enough spells to remove any obstacles that are in the way.
Experiment One | Lotleth Troll | Strangleroot Geist
These are the workhorses of the deck. They'll get onto the battlefield fast and keep the opponent on defense. Strangleroot Geist is great for triggering evolve twice before being recycled from the graveyard. Lotleth Troll is a great way to put a real threat on the board very early in the game. Losing cards to the graveyard isn't really a set-back, especially considering how crazy he can become. Experiment One is a solid evolve creature that is effective for discarding for the troll, evolving early game, or recycling for a cheap token. It also works well with Deranged Outcast
Gyre Sage | Deranged Outcast
These are the utility creatures. Gyre Sage can produce an insane amount of ramp in this deck while becoming a very real threat as it grows. Deranged Outcast is in this deck to die for the cause. He is a great way to grow Gyre Sage or Lotleth Troll, for example.
Corpsejack Menace | Varolz, the Scar-Striped | Kalonian Hydra
If any of these creatures stay on the board, the opponent is in big trouble. Varolz, the Scar-Striped turns the graveyard into token at casting cost, which is very efficient. All of these cheap creatures will be easy to play from the graveyard. Corpsejack Menace doubles the tokens to make massive creatures. Kalonian Hydra is GG almost every time he sees play due to his token doubling ability.
Essence Harvest | Bone Splinters | Golgari Charm
Golgari Charm is a very versatile spell that's useful for removing tokens or chump blockers, in addition to regenerating creatures or destroying enchantments. Bone Splinters is a great kill spell in this deck, since sacrificing a creature isn't a drawback. Essence Harvest provides an alternate win condition to get the last bit of damage through or to buy some time.
Hunger of the Howlpack is probably one of the best spells for this deck. The morbid ability is always triggered in this deck, so it's a very efficient way to add creature counters.
Grim Backwoods helps this deck to keep going later in the game. It's easy to have an empty hand by turn 3 or 4, so this is very useful when top-decking.
