Etherian Mana

Etherian Mana is used to summon Towers and Traps in the Old One's Army event. It has a high chance to be dropped by all of the Old One's Army event enemies. Each wave will produce Etherian Mana in multiples of ten - after receiving a starting amount of ten when activating the Eternia Crystal, each wave will produce either 20 or 30 Etherian Mana. Each Tavernkeep's sentry costs 10 Etherian Mana/Use, so conserving Etherian Mana and developing a strategy is key to the event. This item will disappear after the invasion has ended, along with all event enemies.

Trivia

 * Prior to 1.4.0.1, it is possible to keep the Etherian Mana by placing it in a chest (do not open it again if the event isn't in progress or it'll be lost) before the Old One's Army event ends.
 * However, it is still possible to contain Etherian Mana inside a Money Trough as long as it is not opened if the event isn't active.
 * In the game code, prior to 1.3.5, its name was "its an ammo technically!". Because the actual name was stored in a separate file, this wouldn't display.
 * Etherian Mana is one of the only items that cannot be researched in Journey mode. As such, it cannot be duplicated, the "research [number] more to unlock duplication" tooltip is not displayed, and the researching UI will show an X when it's put in the slot.

History
Mana d'Etheria 天国魔力