Players that have purchased/spend a certain amount of NX may decide to choose from a selection of categories based on their spending. This event will count if you have purchased within April 24 - April 31.
The event consists of three categories for players that will spend a certain amount of NX. These are ranging from 90,000 NX, 120,000 NX, 150,000 NX and will have to choose one set of reward from the category they are in.
Details can be found here: Crokhoon's Treasure Trove Event