Our Lost Brother - A Light Blue Crystal
Roams into the pool where Thistlethought spawns.
Thistlethought drops 6x Essence of Mana, used in A Light Blue Crystal Base.
That's the container from MMM.
Other Pools needed:
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Ragemire Pool <> Essence of Rage Pool
Ragewing roams there.
The Furyfire is the golem that drops 6x Essence of Rage
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Pool of the Dancing Tears <> Essence of Sadness Pool
Tearscale roams there.
The Prancer of Pain is the golem that drops 6x Essence of Sadness.