2 combos in one

[Deebiia]

 {Gravecrawler}  {Carnival of Souls}  {Ashnod's Altar}  {Blood Artist}
I know it's a larger combo, but its low mana cost.
How it works: Play gravecrawler. Have a blood artist, another zombie, carnival, and altar out. Gravecrawler hits you lose a life and get 1 {B} mana. Sacrifice gravecrawler to the altar, get 2 colorless mana while also gaining a life while also causing 1 loss of life to target player. Use the {B} to resummon the gravecrawler. Repeat. (Note: I suggest having 2 gravecrawlers out.)

You can either kill you opponent(s) with the blood artist or, my preference, use all of the colorless mana to cast  {Emrakul, the Aeons Torn} and other eldrazi/colossus spells.