An opponent controls a creature with toughness six or less.
You do not control an Army.
({11} magic symbol) ({R} magic symbol) available.
Steps
Activate That Which Was Taken by paying ({4} magic symbol) and tapping it, putting a divinity counter on a creature an opponent controls with toughness six or less.
Activate Fall of Cair Andros by paying ({7} magic symbol) ({R} magic symbol) , dealing seven damage to the creature that has a divinity counter on it.
Fall of Cair Andros triggers, creating a 0/0 Army and putting at least one +1/+1 counter on it.
When the Army enters the battlefield, Pandemonium triggers.
Holding priority, activate Phyrexian Altar by sacrificing the Army, adding one mana of any color.
Resolve the Pandemonium trigger, dealing 1 damage to the creature with a divinity counter on it.
Repeat from step 3.
Once you have infinite mana, with a Pandemonium trigger on the stack, you may use Fall of Cair Andros' ability to deal infinite damage to the creature with a divinity counter on it, thus causing the Army to have infinite +1/+1 counters on it, which causes the Pandemonium trigger to deal infinite damage to any target.