At the beginning of combat on your turn, Boundary Lands Ranger's ability will check to see if you control a creature with power 4 or greater. If you don't, the ability won't trigger at all. If the ability does trigger, it will check again as it tries to resolve. If you no longer control a creature with power 4 or greater (usually because your applicable creature is no longer on the battlefield), the ability won't do anything.
At the beginning of combat on your turn, if you control a creature with power 4 or greater, you may discard a card. If you do, draw a card.
