Diamonds is one of the three skins released in the third part of the Ark Raider's Mystical Shop offer. It could be collected for free in late September 2018.
Diamonds could be acquired for a limited time in the Skins Shop under the ‘Free’ tab. This skin was not available for purchase and there may be limited opportunities to acquire it in the future.
Details of this skin may vary depending on location, platform or time.
Note: The third part of the Ark Raider's Mystical Shop offer was released again for a limited time in late March 2020. Diamonds could be acquired for free once again.