The controls were a bit clunky, especially the shots from the gun but I liked the idea. I played the game for a while and hit this when I was at a wall on the right wall. Hope it helps.
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ERROR in
action number 1
of Step Event0
for object obj_door_sel:
Unexisting room number: -4
at gml_Object_obj_door_sel_Step_0
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gml_Object_obj_door_sel_Step_0 (line -1)