The artifacts that Jason Blood tells Mary Bromfield not to touch are the Phoenix Gate, the Grimorum Arcanorum and the Eye of Odin. They are the Three Keys to Power from Gargoyles, another Greg Weisman production.
Klarion refers to the events of Misplaced (2012) as a "World without Grown-ups", which was the name of the storyline which lead to the creation of Young Justice in the comics.
This episode's title, "Nomed Esir" is "Rise Demon" spelled backwards. This references both Zatana and Etrigan the Demon. Zatana activates her magic by speaking backwards. And Jason Blood summons the demon by saying "Rise the demon, Etrigan."
The Phantom Stranger dumps Zatanna on the battlefield between the Lords of Chaos; to show just how much safer Klarion is compared to Child.