by Nighthawk » Mon Nov 25, 2013 5:56 pm
The scroll of Create Monster isn't (generally) useful, which is the whole point. It exists as a cautionary tale against reading scrolls willy-nilly without being prepared for the consequences. Many of the game's items exist for the same reason (Potions of blindness, confusion, amnesia; Scrolls of blank paper and sleep; etc.).
Possible uses? Create it at the end of a long room, put it to sleep, polymorph it into something vicious, then kill it from range. Lots of XP.
Can also be used as a rear guard (if it's a weak enough monster) to prevent you from being attacked on two sides by powerful monsters. Aquators are quite useful in this regard, as they don't cause any physical damage.