City of Threads

{t}: Add one {b} or {u}.
{t}, 1 life: Add three mana in any combination of {b} and/or {u}.

Whenever a Nerubian you control dies, you may pay {1}. If you do, create a */1 black and blue Nerubian creature token named Threadling. Its power is equal to mana you made with City of Threads this turn.