Invoke

Invoke is an ability introduced in the Descent of Dragons expansion. When an Invoke card is played, the Hero Power of Galakrond will be activated, as long as the player has a Galakrond hero card in their hand, deck, or battlefield.

Invoke cards are also needed to upgrade Galakrond's Battlecry. Two are needed to upgrade him once, and four are needed to fully upgrade him.

Trivia

 * Adding an Invoke card to your deck without Galakrond while building a Priest, Rogue, Shaman, Warlock, or Warrior deck will display a special text box prompting you if you want to add Galakrond to your deck.
 * Adding an Invoke card to a Druid, Demon Hunter, Hunter, Mage, or Paladin deck has no warning.

Patch changes

 * (Undocumented) Invoke cards can no longer be randomly generated.
 * (Undocumented) Invoke cards can now be randomly generated if you have Galakrond in your deck.
 * Invoke cards can no longer be randomly generated.
 * (Undocumented) Invoke cards can now be randomly generated. They were intended to only be generated by decks with Galakrond in them, but this was not implemented correctly.
 * Added.