(Unstable of the Dead isn't a spell.)
Unstable of the Dead enters the battlefield tapped.
, : Tap target artifact with converted mana cost X or less.
: Add to your mana pool. Unstable of the Dead doesn't untap during your next untap step.
, 
: Tap target artifact with converted mana cost X or less.: Add 
to your mana pool. Unstable of the Dead doesn't untap during your next untap step.
