At the beginning of your upkeep, you gain X life and draw X cards, where X is the number of permanents you own that your opponents control.
{U}{R}{W}: Target opponent gains control of target permanent you control.
If an opponent leaves the game, all permanents you gave to them courtesy of Zedruu will return to your control.
If either the opponent or the permanent you control becomes an illegal target by the time Zedruu's last ability tries to resolve, the ability does nothing.
If you leave the game, all permanents you own leave the game with you.