Create the monster ALL object using the red "monster 3" sprite.
Add an event Collision with wall; then add the following actions...
Add 2 of these monsters in your testing room
Test it out, making sure they creep along the walls like this...
Go into your person object
Duplicate Collision with monster LR ....
Set it to Collision with monster ALL (you don't have to change anything).
Test it out, have your game playing and make sure monsters kill you.