Axis of mortality
Per rules 704 a persons life total becomes zero or less they lose the game. They do not get another upkeep to allow them to use Axis of Mortality ability and cause you to lose the game instead.
[Deleted User] commented
But there are several cards that keep a player from losing that way: Phyrexian Unlife, Pact Weapon, Cloudsteel Kirin, The Book of Exalted Deeds, Platinum Angel, etc.