Disciple of Bolas

Oracle Text

When Disciple of Bolas enters the battlefield, sacrifice another creature. You gain X life and draw X cards, where X is that creature's power.

Card Rulings

7/1/2012 You can’t sacrifice Disciple of Bolas to its own ability, because it says “another.”
7/1/2012 You can’t sacrifice more than one creature this way.
7/1/2012 The ability is mandatory. If you control at least one other creature when the ability resolves, you must sacrifice one. If you don’t control any other creatures at that time, the ability won’t do anything.
7/1/2012 The creature’s power when it was last on the battlefield is the amount of life you gain and the number of cards you draw.