Both will die Neither will die Neither will die Both will die The logic is simple - both creatures have to match the exact colour or exact colour combination
It's also important to note that Marneus's draw effect is not a 'may' ability, and many of our token-producers can be triggered by opponents, so we can lose to your own hubris which, in my opinion, is the best way to lose in Commander
Howling Mine / Font of Mythos / Temple Bell In casual places, we also saw Howling Mine making a hit, followed later by cards like, Font of Mythos and even Temple Bell
Heres the list so far: Major gains (30% or more): Minor gains (10-30%): Chalice of the Void, Noble Hierarch, Through the Breach, Doubling Season, Horizon Canopy, Engineered Explosives, Ancestral Vision, Mox Opal, Crucible of Worlds, Dark Confidant, Scapeshift, Brushland, Fulminator Mage, Ancient Stirrings, Lotus Bloom
and Koaki Meiru Drago can shut down entire strategies