Liliana, Heretical Healer // Liliana, Defiant Necromancer

• WOTC Official Reminder Textofficial rules
  Lifelink — Damage dealt by this creature also causes you to gain that much life.

• WWizards of the Coast2015-06-22
  Official Ruling
  A Magic Origins planeswalker that enters the battlefield because of the ability of its front face will enter with loyalty counters as normal.
• WWizards of the Coast2015-06-22
  Official Ruling
  In some rare cases, a spell or ability may cause one of these five cards to transform while it’s a creature (front face up) on the battlefield. If this happens, the resulting planeswalker won’t have any loyalty counters on it and will subsequently be put into its owner’s graveyard.
• WWizards of the Coast2015-06-22
  Official Ruling
  If a double-faced card is manifested, it will be put onto the battlefield face down (this is also true if it’s put onto the battlefield face down some other way). Note that “face down” is not synonymous with “with its back face up.” A manifested double-faced card is a 2/2 creature with no name, mana cost, creature types, or abilities. While face down, it can’t transform. If the front face of a manifested double-faced card is a creature card, you can turn it face up by paying its mana cost. If you do, its front face will be up. A double-faced card on the battlefield can’t be turned face down.
• WWizards of the Coast2015-06-22
  Official Ruling
  A double-faced card enters the battlefield with its front face up by default, unless a spell or ability instructs you to put it onto the battlefield transformed, in which case it enters with its back face up.
• WWizards of the Coast2015-06-22
  Official Ruling
  The converted mana cost of a double-faced card not on the battlefield is the converted mana cost of its front face.
• WWizards of the Coast2015-06-22
  Official Ruling
  You can activate one of the planeswalker’s loyalty abilities the turn it enters the battlefield. However, you may do so only during one of your main phases when the stack is empty. For example, if the planeswalker enters the battlefield during combat, there will be an opportunity for your opponent to remove it before you can activate one of its abilities.
• WWizards of the Coast2015-06-22
  Official Ruling
  The back face of a double-faced card (in the case of Magic Origins, the planeswalker face) can’t be cast.
• WWizards of the Coast2015-06-22
  Official Ruling
  When Liliana, Defiant Necromancer’s first ability resolves, first you choose a card to discard, then each other player in turn order chooses a card to discard, then all those cards are discarded simultaneously. No one sees what the other players are discarding before deciding which card to discard.
• WWizards of the Coast2015-06-22
  Official Ruling
  Each face of a double-faced card has its own set of characteristics: name, types, subtypes, power and toughness, loyalty, abilities, and so on. While a double-faced card is on the battlefield, consider only the characteristics of the face that’s currently up. The other set of characteristics is ignored. While a double-faced card isn’t on the battlefield, consider only the characteristics of its front face.
• WWizards of the Coast2015-06-22
  Official Ruling
  If multiple nontoken creatures you control die, then Liliana, Heretical Healer’s ability will trigger that many times. However, since Liliana can be exiled and returned to the battlefield only once, only the first ability to resolve will create a Zombie token. The other abilities will resolve but won’t do anything.
• WWizards of the Coast2016-04-08
  Official Ruling
  The back face of a double-faced card doesn’t have a mana cost. A double-faced permanent with its back face up has a converted mana cost equal to the converted mana cost of its front face. Each back face has a color indicator that defines its color.
• WWizards of the Coast2016-07-13
  Official Ruling
  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).
• WWizards of the Coast2017-09-29
  Official Ruling
  You can control two of this permanent, one front-face up and the other back-face up, at the same time.

Rulings via Scryfall