MTG: How can I build 20 mana fast using anyway possible whether artifacts/sorcery/enchantments etc?

I have been playing MTG for a couple of months now and I have LOTS of big, Eldrazi cards for my deck so I wanted to know how I can build my available mana to 20+ FAST in order to use card: Spawnsire of Ulamog special ability: 20: Cast ANY number of Eldrazi cards you own from outside the game without paying their mana costs. Another thing, does that only include those in my deck or any card I may have on hand?