Throne of Bone (Upgraded)

Whenever a player casts a spell, you may pay {x}. If you do, you gain X life and your opponent loses X life.
{2}, Sacrifice Throne of Bone (Upgraded): Tap target creature and add {b}{b} to your mana pool.
"@&%@&$!$***%!!!!"
-An unidentified triggered person who just got pwned by this card.