Im pretty sure that this particular appearance Does appear in the appearance menu.
As of CEP2.3 / 2.4 - they introduced the ability to resize monsters.
eg- Create a Goblin, that is taller than a house etc.
The way you do this, is to select one of the Appearances from the list -(in the appearance list box, not the tail/wings)
It will say Creature_No_Glow etc followed by 100 and small, medium, large, huge etc
Or something along those lines
These appearances are invisible, but when used in combo with tail types that are monster appearances - it will create a Resized Monster of [TAILTYPE]
EG - Set tailtype to be a Balor, and Appearance to be Huge - then you get
Here is an example that I did a while back.