Activate Zedruu the Greathearted by paying ({U} magic symbol) ({R} magic symbol) ({W} magic symbol) , giving control of Altanak to an opponent.
Activate Altanak an arbitrarily large number of times by paying ({0} magic symbol) , targeting itself.
Altanak triggers that many times, causing an opponent to draw that many cards and lose the game due to drawing from an empty library.
Notes
When the opponent loses the game, you will regain control of Altanak. Therefore, if mana allows, you may repeat this combo from step 2 for another opponent.