Ancient Mana

Ancient Mana is a currency used to power certain structures and feed the hunger of several Nightfallen NPCs.

The initial cap is 300, but is increased through use of items and quests, up to 2000.

Ancient mana is a byproduct of underground leylines which has naturally reached the surface. While the result can come in many forms, a crystalline form is the most common.

For Nightborne that are dependent on the Nightwell, it is an effective, if crude, substitute for arcwine.

Source
The quest Ancient Mana (quest) introduces Ancient Mana and the Mana Divining Stone, which applies a permanent, zone-dependent tracking buff that is dispellable. The stone is not needed to keep the buff, only to reapply it. A new stone can be requested at any time. The buff does not involve phasing in any way and you can gather without it, but obviously makes it a lot easier.

At the beginning you will collect Ancient Mana from Ancient Mana Shards. Ancient Mana Chunks and Ancient Mana Crystals, which can drop and, are also found in the wilderness around Suramar City. Mana will also drop from most mobs in Suramar, and when mining and gathering herbs in the zone.

If you fish, you can fish Runescale Koi Pools for Leyscale Koi alongside Runescale Koi, which are worth 25 Ancient Mana each.

Once you complete Masquerade (quest) which unlocks your city disguise, you can move through the city with reduced risk of aggroing guards and it becomes practical to collect Leypetal Blossoms 30 - 50 from the gardens, Glowing Tomes, 55 60 Leypetal Powder, 60 Mana-Infused Gems 55 and bottles of Twice-Fortified Arcwine 100 - 150 from houses and shops.

The Boon of the Manaseeker shoulder enchant, which requires being with The Nightfallen, applies the Manaseeker buff. This causes Mana-Tinged Packs to drop from enemies, which can contain Ancient Mana Shards and.

Cap increasers

 * Enchanted Burial Urn
 * Infinite Stone
 * Kel'danath's Manaflask
 * Kyrtos's Research Notes
 * Volatile Leyline Crystal

Rewards

 * Souvenir Elekk
 * Souvenir Murloc
 * Souvenir Raptor
 * The "Devilsaur" Lunchbox

Daily Feeding

 * First Arcanist Thalyssra
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 * Chief Telemancer Oculeth
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 * Arcanist Valtrois
 * say
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Trivia
According to the comments when fed, Ancient Mana may be necessary, but the taste leaves a lot to be desired. Valtrois describes it as being bitter.