If you don't too bad so sad you lose you get nothing but a mitt full of cardboard. Ok maybe that text is a bit much, but you get it
(It's an artifact with " , Sacrifice this token: Add one mana of any color.") Whenever another creature you control enters, you gain 1 life
As long as you are interested in almost always attacking or sacrificing creatures, Keldon Twilight is worth some consideration
There Once Was a Cycle from Unglued In Unglued , I did a cycle of cards that all had an effect right away and at the start of the next game with the same opponent
(Regular sized for Magic, Pokemon, Race for the Galaxy, Thunderstone, Pandemic, etc.)
Propeller Pioneer Propeller Pioneer has flavor text that makes you want to play it, but in todays EDH, I dont think its even playable if you lop a mana off its casting cost