Itsy's lair is just beyond the sky bridge in the Ravager temple where Blood Twins and Xanados are located. Itsy has an endless amount of adds named Bitsy(s). They all poison, so it is best to keep the adds in check. If the group has a Wizard, they can use Firewall to create a square wall around the group in which the Bitsy will not enter.
Itsy will rarely drop a Poison Protect ring that adds HP regeneration. She will also drop a regular Poison Protect ring and a normal Poison Protect Amulet.