The Eternia Crystal is a consumable item that is used to summon the Old One's Army. It is used much like a Lihzahrd Power Cell, using an Eternia Crystal Stand as its base.
- When the crystal is used, it will appear mounted into the base. It glows during the battle and when the waves are defeated and the event is ending, the crystal will glow its brightest and disappear from the base.
- The price of the crystal increases once any mechanical boss is defeated, and increases again when Golem is defeated.
- The crystal can slowly regenerate health when damaged.
- Defender Medals will drop from the crystal as waves progress, and at the end.
- No longer called "Elder Crystal".
- Added to the game.