Angel Bob informs Alf that they cannot be seen in mirrors because The Tanners cannot audibly hear or physically see them. This effect is based on the supernatural system of Scrooge and the three spirits who visited him in Charles Dickens' "A Christmas Carol".
Alf mentions Michael Landon while he was in the clouds. Landon played an Angel on Highway to Heaven (1984)
The title of this episode is Stairway to Heaven. Alf mentions Michael Landon. Landon plays an Angel in Highway to Heaven (1984) which has a similar title to this episode.