Sip of Hemlock

• WWizards of the Coast2013-09-15
  Official Ruling
  If the creature is an illegal target when Sip of Hemlock tries to resolve, it won't resolve and none of its effects will occur. The creature's controller won't lose 2 life. However, if Sip of Hemlock resolves and the creature isn't destroyed (perhaps because it regenerated or had indestructible), the creature's controller will still lose 2 life.

Rulings via Scryfall