(Green Karoo isn't a spell.)
Green Karoo enters the battlefield tapped.
, : Tap target artifact with converted mana cost X or less.
: Add or to your mana pool.
Put Green Karoo on top of your library: Add to your mana pool.
, 
: Tap target artifact with converted mana cost X or less.: Add 
or 
to your mana pool.
to your mana pool. 
