A fast way of grinding for gems that can get you around 6-7 gems per minute.
Guide to Get Gems
No, it’s not an AFK gem method.
How to Do It
Open up the game (obviously) and then select Local Game > The Arena > VS > Challenge > Solo Challenge. You will need to have the energy orb equipped, but the other weapon doesn’t matter.
Go to door 14 (Soloperation) and complete it as fast as you can. You can do this with any Challenge level but Soloperation is the fastest one for me with a personal best of 24.03 seconds.
Once you’ve beaten the level, press U (replay level) and then spam Enter so that you can replay the level as soon as the option comes up.
To see the speedrun route, watch this video: