This character may join a unit with the Guardians special rule despite having the Fly special rule. As long as the front rank has a minimum of 4 models they may be placed in the second rank. However, they continue to confer benefits to the unit in the form of Leadership and Special Rules. As long as this model is not in base to bae contact with an enemy model, they may cast and dispel as normal, even if its unit is engaged in Combat. However, it may not cast Assailment spells. For the purposes of shooting and casting spells, this model has a 360° vision arc and ignores models in the unit for drawing line of sight.
If the model with this rule is unable to fit neatly into the unit, count its base size as if it were on the correct base size for all purposes for as long as it remains in the unit. IE: a Mage-Priest (50mm x 50mm) counts as having a base of 60mm x 60mm when it joins a unit of Temple Guard (30mm x 30mm). To achieve this, you may use a spacer, or simply leave room to either side of its base on the movement tray so that rear ranks can close around it correctly.