First of all, I would not recommend watching this short if you haven't seen The Outwaters. This is intended as a prologue to that film, and without that context it will probably seem fairly bland and pointless. Essentially it's a short story about a budding relationship where a few weird things happen.
If you saw and enjoyed The Outwaters and are looking to dive deeper into the lore, this short, along with the epilogue, File VL-624, delivers that in small doses. Card Zero gives more context around the friends' reason for traveling to the desert, as well as Robbie's state of mind going into The Outwaters. It also hints at how the "entity" first comes into his life.
It serves its purpose as a prologue well, providing context around the setup of the premise that clarifies some things about The Outwaters, and made me appreciate it more as a result.
