The guide knows all the shortcuts the caster does, but will not always use them first try! At the DM's discretion, the guide can lead a group into nearly any situation as long as it is conceivably 'on the way' to their next location. If the situation forces the group to retreat, the guide can conveniently reveal an alternate route that would have gotten them there also--usually much faster.
Because it transposes the mage with their reflection, the caster reappears as a mirror image of their self, including transposing their handedness and other such features. The next use of this spell will restore them to their natural orientation. This is not obvious to a character reading the spell from a scroll or book, but causes no penalties or bonuses.
Casting this spell on a mirror will put the caster into the border ethereal, that portion of the ethereal plane which overlaps the Prime. This effect is similar to the spell etherealness, with two important exceptions stemming from the fact that the caster is slightly out of phase with both the Prime and Ethereal planes.
DMs who wish to tone this spell down may wish to make changes such as the following:
Or anything else the DM can think of.