Doomsday is one of the four skins released in the Doomsday offer. It could be purchased on an individual basis using game coins in late April 2021.
Doomsday could be purchased in the Skins Shop under the 'Doomsday' tab for 3300 coins. It was available for a limited time and may not return in the future.
Details of this offer can vary depending on location, platform or time.
Note: Doomsday was also released early as a part of an Amazon Prime deal.