El Diablo belongs to Lana, and lives in her and Lola's room, greeting new people by wrapping himself around them, and squeezing them tight. However, this nature tends to chase off guests that feel threatened by him.
El Diablo is a standard looking green snake with yellow spots.
This is not technically true as a snake is shown in the scene where Lincoln tries to ask Lana to sleep in her bed. That snake could have been El Diablo or a new one. But in "Fool's Paradise", she mentions El Diablo when she asks god to prey to take care of the pets. This means Lynn Sr. could've meant another snake because in "Come Sale Away", she had a bunch of other snakes rather than El Diablo.