Havengul Lich

• WWizards of the Coast2011-01-22
  Official Ruling
  Havengul Lich’s activated ability creates a delayed triggered ability that triggers when you cast the creature card. This triggered ability will go on the stack on top of the creature spell and will resolve before the creature spell will.
• WWizards of the Coast2011-01-22
  Official Ruling
  If you don’t cast the creature card that turn, Havengul Lich won’t gain any of its abilities.
• WWizards of the Coast2013-04-15
  Official Ruling
  Havengul Lich’s ability changes the zone you are permitted to cast the card from, not the times you are permitted to cast it. You can cast a creature card that has been targeted by Havengul Lich from the graveyard, but unless it has flash, you can only do so if it’s your main phase, the stack is empty, and you have priority.
• WWizards of the Coast2016-06-08
  Official Ruling
  Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text.
• WWizards of the Coast2019-10-04
  Official Ruling
  Havengul Lich gains the activated abilities of the card as it existed in the graveyard while that card is still a spell on the stack.

Rulings via Scryfall