Cerebro 3 is great and all, but the biggest weakness isn't in its synergies, but its consistency. After watching 23 Cerebro 3 videos and livestreams, I've seen so many instances of locations messing up people's on-the-board energy, (like Sewer System, Monster Metropolis, Negative Zone, and nidavellier as examples). And in those instances there are people who have already used rhino and magik to get rid of those locations (which are here). However, locations still exist which mess up your card power directly (like Wakandan Embassy, The Peak, Stark Tower) or have permanent effects on cards even after you change the location (like Muir island, Shuri's Lab, Jotunheim). Shadow King is an amazing way to get that extra consistency of resetting your power, similar to Valkyrie but for less cost. It makes keeping your Cerebro synergy more consistent. With this deck you get more consistency for everything: Location changers like Rhino and Magik, Disruption/Protection cards like Armor and Cosmo, Lockdown cards like Juggernaut and Professor X, Power Reset cards like Shadow King and Valkyrie, Consistent plays like Colossus and Sentinel, and then your main archetype Cerebro. I unlocked Shadow King as a F2P through my caches and I can confirm that Shadow King is one of the best cube equity cards because nobody ever expects it.