Bone Fetish are undead versions of normal Fetish and can be encountered in various dungeons and temples of Act III of Diablo II, as well as in the Worldstone Keep in Act V in Nightmare and Hell Difficulty and in the Durance of Hate, levels 1-2.
Though their bodies are fragile they move at an incredible speed and deal high amounts of damage: it's best to kill them as fast as possible. However, they have one additional feature that makes them even more lethal: upon death they explode, dealing even more damage. This makes Bone Fetishes one of the most dangerous monsters in the game, especially when found in a group.
The exploding damage is based upon the amount of life they were spawned with. When playing with a full party, be warned, as the damage potential could be a severe. Freezing them with Cold attacks and finishing them off from a distance is one way to deal with this. Hirelings are also immune to the Bone Fetish death explosion, so Act II and Act V Hirelings, who use melee attacks can help keep them at a distance, might be another method of dealing with them.
Blizzard made an interesting decision here, even though the Bone Fetish explode when killed, they give massive amounts of Experience. This sometimes puts players in a dilemma over whether to kill them and reap the benefits or try to kill them and be killed, or at least heavily damaged.
A player can turn into level 50 Bone Fetish when hit while wearing a helmet enchanced with Delirium Rune Word.
"Although the Fetish Shaman has the power to bring back fallen Fetish from the grave, not every casting of this spell returns them as their former selves. Corpses that are too old to be fully restored often rise again as undead shades of the Fetish. While still useful, the form of a Bone Fetish is also quite unstable, causing it to explode violently when destroyed."