One of the more useful NetHack tools. A Bag of Tricks is basically filled with monsters in fuzzball form. Taking one out ("apply"ing the bag) creates a random monster. A Bag of Tricks is generated with 1d20 charges. As long as charges remain, applying the bag has a 22/23 chance of creating a random monster and a 1/23 chance of creating 2d4 monsters.

When you try to #loot the bag for the first time, it will sprout a vicious set of teeth and bite down on your hand for 1d10 points of damage -- this of course identifies the bag (but it can be deadly at low levels, and this is an embarassing way to die). A Bag of Tricks can be recharged by a scroll of charging. When the bag is out of charges, it becomes completely useless until recharged.