Rhiannon Heen

Rhiannon Heen was a substitute homeroom teacher at Kings Elementary and came from Salem, Massachusetts. She is described as having angelic beauty and power.

She has helped the griffins out a couple times, once when they were confronted by Morgan LaFey on the hilltop she came between The Griffins and Morgan and provided the diversion they needed to get the Codex back. After the battle she disappeared and wasn't seen again until the end of the third book at the Griffin's award ceremony where Max and his friends saw her appear in the chapel in a blinding flash of light.

Powers: Levitation

Light Manipulation

Geokinesis

Pyrokinesis

She has definitely proved herself to be Morgan LaFay's equal as neither of them gained the upper hand in their battle.

Who is she really: Though this has never really been confirmed she may be a white witch. The clue being her previous residence, a very powerful faerie, or she may in fact be Titania herself. This also was never denied or confirmed though.