Vampire Nocturnus

• WWizards of the Coast2009-10-01
  Official Ruling
  To work as an evasion ability, an attacking creature must already have flying when the declare blockers step begins. Once a creature has become blocked, giving it flying won't change that.
• WWizards of the Coast2013-04-15
  Official Ruling
  When playing with the top card of your library revealed, if an effect tells you to draw several cards, reveal each one before you draw it.
• WWizards of the Coast2013-04-15
  Official Ruling
  The top card of your library isn't in your hand, so you can't suspend it, cycle it, discard it, or activate any of its activated abilities.
• WWizards of the Coast2013-04-15
  Official Ruling
  If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, the new top card won't be revealed until you finish doing so.
• WWizards of the Coast2013-07-01
  Official Ruling
  If the top card of your library is black, Vampire Nocturnus will give itself +2/+1 and flying even if it's somehow not a Vampire.

Rulings via Scryfall