Valkyries Fall

From the action menu, you will find the Mission Center. Here you can select a particular monster to kill repeatedly for a reward.

Simply select the monster that you want to kill (read: strongest you can kill) and keep attacking them until you’ve met your mission quota, then return to the mission center to claim your reward and start a new mission.

Monsters must be slain on the same plane that you began the mission, regardless of their names.

Currently, there are two types of mission but functionally they are the same.

• Kill missions require you to kill as many enemies for completion.
• Collect missions require you to collect items dropped by that enemy for completion. 
• You need 10% as many items from enemies as you do kills from kill missions,
  but they have a 10% drop rate, so it’s roughly even with a little bit of RNG.
  
  

Completed missions normally reward gold.
However, every five missions that you complete will earn you diamonds instead!

Every time you complete a mission, the next mission will require approximately 10 more kills (or one more item) to complete. However, you will also earn increasingly more gold and/or diamonds than the previous reward. That is to say: although the number of kills required increases, so too does the reward. Every diamond mission you complete will earn you one additional diamond than it did previously.

Missions are incredibly important. You ideally want to continuously be doing missions while playing due to the scaling nature of their rewards and importance of diamonds.