Supremus is one of the three skins released under the Ancient Knight part of the Mechanos offer. It was available for purchase in late June 2017.
Supremus could be purchased for $4.99 in a deal that included 3250 coins. It could also be purchased for $19.99 in a deal that included the Mechatron skin and either 50000 coins (Browser) or 1800 DNA (Mobile). It was not available for individual purchase and may not be available for purchase in the future.
Details of this offer may vary depending on location and platform.