PISORF ("Piss Off") is one of the Glyphs you can find in a game of Desktop Dungeons. When used, this Glyph teleports the target monster to a random tile in the dungeon. This Glyph may spawn randomly in any dungeon and does not need to be unlocked.
PISORF is cast by clicking on it, and then clicking on the monster you wish to target. That monster will be the target for the PISORF effect.
When PISORF is used on a monster, the game first randomly chooses one empty tile from anywhere in the dungeon. It then teleports the targeted monster to that tile.
Any monster is valid as a target for PISORF, regardless of its level. You may even target the Bosses, and they will indeed be moved. Note however that if the target monster has any Magic Resistance, it has a chance to resist the spell entirely, causing a normal failure (Mana wasted, no effect). The chance of this happening is equal to the monster's Magic Resistance value.
Any empty tile may be randomly selected as the target of the teleport. "Empty" here means any tile your hero can freely move through. This excludes wall tiles, or tiles containing monsters or plants, but including Altars, Shops, or tiles containing Glyphs or blood-stains, etc. Note that this includes unexplored tiles! The monster might even be teleported into a part of the dungeon you cannot currently reach (for example, an rear blocked on all sides by other monsters). As long as the target tile itself is empty, it is a valid choice for the spell.
Rarely, the game might teleport the monster to the same tile it is already standing on. This is still considered a fully-successful use of the Glyph, and so will cost you Mana and trigger relevant effects as normal.
PISORF is unlocked from the moment you create a new Profile. It has a certain chance to appear in each dungeon you play, supposedly the same chance as any other unlocked Glyph (though this has yet to be proven conclusively).
PISORF is not a generally-useful spell, and can't be described to play a part in any actual strategy. Its effect is only required in very specific circumstances, and is pretty much useless in all others.
Normally, PISORF is used to remove a monster which is blocking your progress into the rest of the unexplored dungeon, or towards an item or other monster. Therefore, it is used when taking out the blocking monster is not possible, or not desired.
Situations where it is preferable to move the monster rather than kill it include cases where you have set up a mid-fight level-up and still want to do more exploration, but a monster is blocking your path to unexplored tiles. Killing said monster will level you up "for nothing", and so it is preferable to simply move that monster away and perhaps kill it later. Another similar situation is when your character specializes in killing monsters of much higher level than his own, or benefits from leaving many lower-level creatures alive in the dungeon for the later stages. In such a case, lower-level monsters are moved instead of killed whenever they are encountered blocking a passage through the dungeon.
Due to its highly-specialized usefulness, there is no benefit to pairing PISORF with any other spell. If you wish to keep PISORF at all, it's usually just an extra ability you store for emergencies, if they arise, regardless of what other Glyphs you may or may not have.
PISORF and the Gods
Several Gods in the game have various opinions about the use of PISORF - they may favour it or reject it, depending on their own particular creeds.
The Trickster God appreciates the use of under-handed means, and considers PISORF to be one of those means. As such, he will reward you +1 Piety point for each use of the PISORF Glyph.
As with any other Glyph, Turog will penalize you -5 Piety points every time you use PISORF.
Mystera Annur will increase your piety by +1 for every use of PISORF. This includes cases where the target has resisted the spell (through Magic Resistance).