This spell will create a random rather low lever monster. It won't however increase your casting skill, as it is a Level 0 spell.
The Monster created will be determined by chance, dungeon depth and what area the spell is used in. There is a high chance of creating Gnomes in the Gnome Mines or a Roman in the Roman Fort. At 100 feet, Garter Snakes, Rats, Goblins and Kobolds are usually created, whilst Orcs and other higher level monster will begin to be created deeper down.
It is a very handy spell for any character to have, since it can be great in many scenarios: