there the only 3 items that restore hp every turn but black sludge is best for a poison
shell bell is best for aron fear set :) -shell bell recovers 1/8 damadge done to the opponent
leftovers - recoveres 1/16 of hp every turn
black sludeg - same as leftovers recovers 1/16 hp If the holder is a Poison-type, it will recover 1/16th of its maximum HP rounded down at the end of each turn. All other types will take damage equal to 1/8th of their maximum HP if holding this item. - from smogon
so if annoying pokemon such as jirachi use trick there in for a nasty supprise so defintly go black sludge but there are certain abilitys that can recover hp each turn such as ice body
