Rustle is a spider-like creature with a large upsidedown head with two antennas on it for a torso. Rustle is very fast and aggressive and will chase the player around the room. It attacks by firing shots from its antennas and will occassionally stop to shot from its mouth, similar to Dobee.
Upon entering the room the player will have to kill 2 Gileads which spawn in the corner of the room and Rustle himself. It is important that the player kills the 2 Gileads or they will find themselves taking a lot of damage by way of random bullets from off screen. After you are done killing 2 Gileads then it's time to focus on Rustle himself. If you are fast enough then you can do circles around the room while keeping a safe distance from Rustle.
This boss was designed to look like the Thing from the 1982 version of The Thing and was named after the lead actor Kurt Russell (Source: Developer Travis Pfenning)