# Phasing
Phasing is the ability to walk through solid tiles, such as walls and boulders. The property is possessed by xorns, earth elementals, ghosts, and shades.[1] This does not allow one to cross pools of water, or walk through those rare areas that are designated as non-phasing: all of Sokoban, a dividing wall in Moloch's Sanctum,[2] the inner wall around the Wizard's Tower, and the entire Astral Plane. In Sokoban, phasing players (but not monsters) are prevented from moving through boulders on a level until the puzzle is solved.
The only ways to gain phasing are to polymorph into a xorn or earth elemental, or to pray while stuck in a wall. Being stuck in a wall is considered a major trouble, and a successful prayer will normally teleport you to a safe position, but it will grant phasing for 4d4+4 turns instead if the teleportation fails.

Contents

1 Strategy
2 Messages
3 Variants

3.1 SLASH'EM
3.2 Convict patch
3.3 FIQHack

4 References

Strategy
The use of polymorphing into a phasing monster to gain a combat advantage is dubious, as neither the xorn nor the earth elemental is particularly tough. Xorns cannot wear body armor or cloaks (these will be destroyed upon transforming), and earth elementals cannot wear anything. 
Phasing may be used as an alternative to digging, especially for accessing items embedded in walls, or retreating if you're getting surrounded. It can also be used situationally to approach a shop from across an unmapped level and steal from it.
Strategically, phasing can be used to quickly bypass some areas of some maps. It is one way a Rogue can solve their final quest puzzle. Some players will polymorph into a phasing creature for Gehennom mapping to make the search pattern simpler; walking on the walls helps avoid traps.
Speed runners strive to phase into the correct turret of the Castle, and from there to the gem chamber (for Luck) and the trapdoor to the Valley of the Dead. The Valley, Asmodeus' Lair, and Vlad's Tower can be noticeably abbreviated with phasing. However, phasing is not a universal solution to non-teleport mazes, because xorns are slow and the lack of a cloak makes it dangerous to fight level draining monsters, shades, or Yeenoghu.

Messages
You feel much slimmer.
As a result of prayer, you temporarily gained the ability to pass through walls. This happens if you were stuck in a wall, but there was no safe place to teleport you to.[3]
You start to feel bloated.
You can temporarily pass through walls, and the power will wear off in 4 turns.
You are feeling rather flabby.
You can temporarily pass through walls, and the power will wear off in 2 turns.
You're back to your normal self again.
Your temporary phasing power wore off, you are not stuck in a wall, and you are not hallucinating.
You're back to your unusual self again.
Your temporary phasing power wore off, you are not stuck in a wall, and you are hallucinating.
You feel hemmed in again.
Your temporary phasing power wore off, and you are still stuck in a wall.
Variants
SLASH'EM
SLASH'EM introduces the spellbook of passwall, which gives the caster phasing for 50–149 turns.

Convict patch
UnNetHack, Slash'EM Extended, SlashTHEM, dNetHack, DynaHack, SpliceHack, and EvilHack introduce the Iron Ball of Liberation as the Convict quest artifact, which grants temporary phasing when invoked.

FIQHack
FIQHack introduces the level 7 spellbook of phase which gives the caster phasing for 21-60 turns.

References

↑ It is indicated by M1_WALLWALK in monst.c

↑ In NetHack 3.4.3, it had a gap at the upper edge of the map.

↑ src/pray.c in NetHack 3.6.1, line 427

This page may need to be updated for the current version of NetHack.
It may contain text specific to NetHack 3.6.1. Information on this page may be out of date.
Editors: After reviewing this page and making necessary edits, please change the {{nethack-361}} tag to the current version's tag or {{noversion}} as appropriate.