2011-01-22 : If you activate one face’s ability, and some effect causes the card to transform twice that turn, you won’t be able to activate that face’s ability again that turn.

2011-01-22 : You can activate Wolfbitten Captive’s ability, let it transform into Krallenhorde Killer, then activate Krallenhorde Killer’s ability, all on the same turn, and vice versa.

2016-07-13 : For more information on double-faced cards, see the Shadows over Innistrad mechanics article (http://magic.wizards.com/en/articles/archive/feature/shadows-over-innistrad-mechanics).