- Main article: Bestiary
Invisible monsters are some of the most annoying to deal with, especially when you are alone on a floor with them. Fortunately, these tend to be relatively rare and weak. One way to deal with invisible monsters is to throw potions or water at them, since they are visible when wet. They are always visible during rain for that same reason. However, if you can't finish them off shortly, they become invisible again after their wet status gone.
Another way to locate the invisible monsters is to use the target key "*". Target every tile from the direction of the throwing potions until the text "You target something" appears. That tile is the exact position of the monster. You may fire from distance, or cast spells of bolt/ball to kill it. Spells of dart/arrow won't work though when they are invisible.
The only way to see invisible monsters is to wear equipment with property "it allows you to see invisible creatures". Two fixed artifacts have this property: the Sage's Helm can be bought from Miral and Garok's Workshop for some small medals and the Lucky Dagger is granted as a final reward by deity Ehekatl of Luck. Random artifacts that allow you to see invisible are sometimes generated, too.
Types of Invisible Monster
Pumpkins are not that strong, are not necessarily always invisible and are capable of being extremely dangerous. They throw various potions which include status effects, mutations, cure mutation and weaken resistance. The best way to deal with these is to watch where the potion is being thrown from and throwing a potion on that location. If this cannot be done figure out what direction the potions are coming from and use melee attacks to find the Pumpkin's location and kill it. The Pumpkin will eventually stop being invisible and/or get drunk or land in a pool of acid, causing it to cease being invisible.
Weaker version of the pumpkin. Looks just the same, however.
Stronger version of the pumpkin.
Even stronger version of the pumpkin.
Stalkers are permanently invisible melee attackers. They do a decent amount of damage and have quite a bit of HP. Since they are invisible, you cannot shoot them and must weed them out with melee attacks. Another way to deal with them is to walk down a one-square corridor, throw a potion right on the square behind you, and continue down the path; the stalker will step into the puddle whilst following you, revealing its form.
Eating a stalker corpse may grant you some Darkness resistance.
Stronger version of the stalker.
Eating a shadow stalker corpse may grant you some Darkness resistance