It is by far the rarest piece of its set.
Aside from its chance to activate the Enchant spell, Immortal King's Soul Cage's stats are unremarkable when the armor is worn individually. However, it becomes a formidable piece of armor when used with the rest of its set, boosting all resistances, having a high hit recovery, and high defenses.
Its very high strength requirement may seem prohibitive, but it is alleviated somewhat by the big strength bonuses given by some of the other items in the set.
Immortal King's Soul Cage
Defense: 1001 (Base Defense: 487-600)
Defense: 1301 (Base Defense: 487-600)
Required Level: 76
Required Strength: 232
25% Faster Hit Recovery (2 Items)
Cold Resist +40% (3 Items)
Fire Resist +40% (4 Items)
Lightning Resist +40% (5 Items)
+50% Enhanced Defense (Complete Set)