Halo Wars: Definitive Edition

Play a standard game on any map as a Covenant leader. Focus on building warehouses and a temple. It is a good idea to build a few smaller units and turrets in case the enemy attacks as getting Scarabs can take a while. Once you have a few smaller units, go after a second base and start building more warehouses and upgrading them.

Once you have enough supplies, focus on advancing your tech level through the temple and also researching Followers. Once you have your total capacity at 50 and at least 40 population spare you need to build two scarabs. Once both Scarabs are on the battlefield, use them to destroy your enemy/enemies and once you have won, the achievement will unlock.