An opponent controls a creature with toughness less than 13.

Cast Blasphemous Act by paying at most , dealing 13 damage to each creature.
For each creature opponents control that is dealt excess damage, Fall of Cair Andros triggers, creating a 0/0 Army if you dont control one, and putting a number of +1/+1 counters on an Army you control equal to the excess damage.

Gilraen does not have summoning sickness.
Creatures you control can tap to produce at least .

Activate all mana-producing creatures you control by tapping them, adding at least .
Activate Gilraen by paying and tapping it, blinking Village Bell-Ringer.
When Village Bell-Ringer enters the battlefield, it triggers, untapping all creatures you control.
Repeat.
If creatures you control can tap to produce at least , this combo nets infinite mana.