Rulings

• 2021-06-18
  Tribal is a card type that allows noncreature cards to have creature types. Altar of the Goyf is a Lhurgoyf (although not a creature) while on the battlefield, and a Lhurgoyf card (although not a creature card) in zones other than the battlefield.
• 2021-06-18
  A creature attacks alone if it's the only creature declared as an attacker during the declare attackers step (including creatures controlled by your teammates, if applicable). For example, Altar of the Goyf's first ability won't trigger if you attack with multiple creatures and all but one of them are removed from combat.
• 2021-06-18
  The card types that can appear in a graveyard are artifact, creature, enchantment, instant, land, planeswalker, sorcery, and tribal. Legendary, basic, and snow are supertypes, not card types; Aura and Lhurgoyf are subtypes, not card types.
• 2021-06-18
  If Altar of the Goyf somehow becomes a creature and the effect allows to keep its other types, it will give itself trample.