What's a good horde mode game without a resource to grind? In Call of Duty: Black Ops Cold War, players will want to find ways to earn raw aetherium crystals. These crystals are a new resource for players to keep track of, and based on what Treyarch has shared, it looks like it's exclusive to the Zombies mode. Without them, players who want to reach the highest and hardest levels where massive waves of undead horde await them are likely going to find themselves struggling to survive. What do raw aetherium crystals do? These will be how you upgrade your skills and perks in Zombies mode. These skills include your field upgrades, ammo modes, weapon classes, and perks given to your character. For those who want better chances of taking down the tougher zombies they encounter closer to the end of the rounds, you want to have a good chunk of these crystals to spend on your ideal build. Earning raw aetherium crystals will be important. So far, we know of two ways you can earn these crystals. The first is by reaching milestone rounds in the Zombie mode. We don't know what numbered rounds these are, but it's likely after surviving a certain wave of zombies that include various special ones and bosses that you and your team have to fight. It's likely that after you beat them, you can earn your crystals for the next playthrough. The other method is to exfiltrate successfully. You can exfiltrate a Zombie mode after round 10, and then every five rounds after that, you and your team have the option to do this. The various perks and skills you upgrade in the Cold War Zombies mode will take time, but the further you and your squad go each time, the more rewards you receive. The perk upgrades are permanent, so you won't need to upgrade at the start of every new round.