Ritual Pendulum Monsters are a special kind of Pendulum Monster that also count as a Ritual Monster, therefore are placed face-up in the Extra Deck when sent from the field to the Graveyard, and can then be Pendulum Summoned provided they were properly Ritual Summoned at first.
Unlike other "hybridized" Pendulum Monster kinds, which are to be Summoned from the Extra Deck, Ritual Pendulum Monsters can exist in the hand and therefore can be placed in a Pendulum Zone as a Pendulum Scale without needing card effects, making their nature actually benefit them, though with the downside that they cannot be Summoned anymore unless returned to the hand and then properly Ritual Summoned, or if a card that allows Ritual Summoning from the Pendulum Zone is available.