Pearls of Wisdom are forging materials that can be used at an Enchanted Forge to unlock a fourth stat on gear.
You will need a Chaos Forge to use Tentacles of Q’bthulu. They can be obtained by completing Shadow Towers and active tomes. They used to rarely be found in chests in Uber worlds and they can be dropped by Shadow Giant.
They used to be available in the Store, Shadow Caches and from Shadowy Treasure Isles Traders, but were removed.
To get maximum upgrade on item you will need 11 Pearls of Wisdom. First 3 pearls adding stat to the item, and other 8 will increase the value of stats up to the 30%.