In Deadman's Shadow, there is a chance of encountering a Big Dog in the place of a monster in either of the two maze areas. Only one Big Dog can appear per room and can't appear in a room with a Night Fright.
These Big Dogs are considered sub-boss level monsters and Resist all Crowd Control.
They also have an attack that Roots the player in place. When that happens the Big Dog will ignore whoever is rooted and attack the other players.
Its attack is a larger AoE than other enemies.
It tends to ignore people on higher or lower elevation.
It can be reset like any other enemy.
In Green Rooms it's usually the first or second enemy type to kill, depending on if they're bats in the room.
Be careful not to accidentally attack the Big Dog while someone is kiting. They'll attack if they're anywhere close to the kite and then the kite will lose aggro for a few seconds.