Flying, indestructible Kefnet the Mindful can't attack or block unless you have seven or more cards in hand. {3}{U}: Draw a card, then you may return a land you control to its owner's hand.
2017-04-18
Once Kefnet has attacked or blocked, it will remain in combat even if the number of cards in your hand becomes six or fewer.
2017-04-18
While resolving Kefnet's activated ability, you don't choose which land to return to its owner's hand (or whether you'll return one at all) until you see the card you draw.