(Rootbound Tower isn't a spell.)
Rootbound Tower enters the battlefield tapped.
, : Tap target artifact with converted mana cost X or less.
: Add to your mana pool. If you played a land this turn, Add to your mana pool instead.
, 
: Tap target artifact with converted mana cost X or less.: Add 
to your mana pool. If you played a land this turn, Add 
to your mana pool instead.
