Delirium grants a proc that, when activated, transforms the caster into a level 50 Bone Fetish for roughly 60 seconds. The newly transformed Fetish's normal attack is a headbutt. While Delirium can be made in any type of helm and can be used by any class, it is best used by a Druid since he can transform back from this Fetish form by using the Werewolf or Werebear skills.
For this reason, Delirium should be made in a Druid Pelt that provides bonuses to key Elemental Skills, such as a pelt having +3 to Tornado and +3 to Cyclone Armor. This will give the player a bonus of 5 skill levels to their most used skills.
Besides the potentially great bonus to skills if used in the correct base pelt, the other modifiers on Delirium are pretty lackluster. Jalal's Mane is arguably an overall more useful helm, especially since it can be socketed with an additional rune or jewel for further item bonuses and customization and won't force the player to put an unnecessary skill point into Werewolf. These advantages may outweigh the extra skill bonuses potentially offered by Delirium.
However, no matter how good the base pelt is for Delirium, it is quite possible to find an even better Rare Druid Pelt that provides bonuses to Druid Skills, Faster Hit Recovery, Life, 1-2 Sockets (which can be then be used for All Resistances, more Life and/or more Faster Hit Recovery) and +3 to Tornado (or another desired skill). Of course, finding or trading for such a rare pelt can be quite difficult, so Delirium or Jalal's Mane can act as temporary helm in the meantime.
Looking beyond Druids, Delirium is also a possible choice for a mercenary. Aside from the Iron Wolves (who need to cast spells), the Bone Fetish transformation is much less debilitating to mercenaries. It offers next to no mods that are useful for them personally (since they also do not benefit very much from +skills), but it does throw disruptive curses all over the place, which can be greatly helpful for keeping hostilities away from the player themselves. However, if the player is reliant on any curses of their own, Delirium can annoyingly overwrite them.
1% Chance To Cast Level 50 Delirium When Struck (morph)
6% Chance To Cast Level 14 Mind Blast When Struck
14% Chance To Cast Level 13 Terror When Struck
11% Chance To Cast Level 18 Confuse On Striking
+2 To All Skills
+10 To Vitality
50% Extra Gold From Monsters
25% Better Chance of Getting Magic Items
Level 17 Attract (60 Charges)