Instructions:
1. Find the rare Dr Witherlimb in one of the ziggurats in the Ghostlands.
2. Get his debuff "Withering Poison" on you.
This is the only way I know of shrink my character for low-level pvp.
It is also the only way I know of to shrink a hunter pet or other minion
without damaging their stats too much.
Currently does not seem to work for high-level characters.