Flying, indestructible
Kefnet 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.
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.
18 Apr 2017
Once Kefnet has attacked or blocked, it will remain in combat even if the number of cards in your hand becomes six or fewer.