The Emerald Queen first appears in the Pharos of the End.
The Emerald Queen's chapter first appears alongside the rest of the other Truths, but in Pharos of the End II, she is able to really make her appearance known. She appears before August Asclepius Averruncus, aiding him on his quest to restore Chaos. It is even explained that she had blocked many truths from being interfered with. Later, she is the cause for Christopher Sincere Pride's defeat.
Powers and Abilities
The Emerald Queen is a necessary existence, and a necessary presence. It transcends names and terms -- and in essence is unknowable. The Emerald Queen stands as the concept of an "infinity" that transcends the transfinite numbers. Because there is nothing else to have ever created it... if it had ever 'not been,' even for a moment, THE ALL would not 'be' now. It is a necessary existence that was not finite, changeable, fleeting, or conditioned.