Board Thread:Fun and Games/@comment-19062822-20140209003329/@comment-19062822-20140216072831

Auracrist - Use 50 Auracrysts on a really hard to get tower (Towers that are pre-brought don't count).

Difficulty: Depends on how fast you can get an Auracryst.

Game: BTD6

Event: The Auracrysts combine into a huge Auracryst.

Reward: You get the Ultra Auracryst for future use (The achievement resets after using the Ultra Auracryst.).