London Bridges

London Bridges enters the battlefield tapped or
with a bridge counter on it
{t}: Add two mana of any color. Spend this mana
only to cast permanent spells. Permanent spells
cast this way enter the battlefield with a bridge
counter on them.
Whenever London Bridges becomes tapped, roll
a d10. Sacrifice all permanents you control with
bridge counters that have mana value less that or
equal to the results. All other permanents with
bridge counters get a shield counter.