The polyself bug is a fairly serious flaw in the handling of a self-polymorph by an experience level one character. It is listed as SC343-10:
SC343-10: Player can raise HP and Pw by dancing with vampires.
In order to exploit this bug, a player would need to drain life themselves to reach experience level one, whether by the spell, by throwing a level-draining weapon upwards, by the attack of a level-draining monster, such as a wraith or vampire (as alluded to in the official description of the bug), by praying repeatedly, or by using any other method of level loss.
Once this is done, the act of self-polymorph has a chance of adjusting a player's experience level. If self-polymorph increases the player's level, his hit points and power are approximately doubled or tripled[1], which is not offset by the act of draining this level. Therefore, by repeatedly polymorphing and draining level back to one, a player's hit points and power can be increased to the limit of (usually) a 32-bit signed integer.
The act of self-polymorph also has a chance of killing the player if his level drops to zero; therefore, in order to obtain a significant amount of HP and power, a handful of amulets of life saving is recommended. Pudding farming is often used to acquire a healthy quantity.
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