This tutorial was a thread before, so credit goes to marty22 for bringing this up into the forums, im just posting this in the tutorials section because i believe it deserves recognition as it is for singleplayer.

Basically your Enemy ai will hide behind a door and open to shoot out of it and then hide behind it. Think of the mission blackout when you save nikolai, right before u get to him theres a guy hiding behinid a door and opens it just a bit to shoot out at you, then hides behind it again.

1) place the misc_prefab of "door_hiding_open.map" or "door_hiding_closed.map" into your map wherever u want this event to happen.

2) Place an AI on the inner part( thats the part the player cant get to him )

3) check "spawner" on the ai and "forcespawn"

4) give him key/values of "script_noteworthy"/"hidding_door_spawner"

5) spawn ur ai via a trigger or script. Thats up to you.

6) OPTIONAL:

i) place key/values of "script_flag_wait"/ your_flag. You'll
have to call the flag at your discretion.

or

ii) Dont give him a flag and he will start shooting when you get
near him.

Make sure that you have thisin your mapname.gsc right before the _load::main(); :

maps_hiding_door::main();

and in your zone file make sure u have the right stuff added, which should be something like this:

rawfile,animtrees/script_model.atr
rawfile,maps/_hiding_door.gsc

xanim,doorpeek_open
xanim,doorpeek_kick
xanim,doorpeek_jump
xanim,doorpeek_idle
xanim,doorpeek_grenade
xanim,doorpeek_firec
xanim,doorpeek_fireb
xanim,doorpeek_firea
xanim,doorpeek_deathb
xanim,doorpeek_deatha
xanim,doorpeek_close
xanim,exposed_idle_twitch_v4
xanim,exposed_idle_twitch
xanim,exposed_idle_reacta
xanim,exposed_idle_reactb
xanim,combat_jog
xanim,patrol_jog
xanim,patrol_bored_patrolwalk
xanim,patrol_boredwalk_lookcycle_b
xanim,patrol_boredwalk_lookcycle_a
xanim,patrol_boredrun_find
xanim,patrol_boredjog_find
xanim,patrol_boredwalk_find
xanim,patrol_bored_react_look_retreat
xanim,patrol_bored_react_look_advance
xanim,patrol_bored_react_walkstop_short
xanim,patrol_bored_react_walkstop
xanim,patrol_bored_react_look_v2
xanim,patrol_bored_react_look_v1
xanim,patrol_bored_2_walk_180turn
xanim,void_loop
xanim,german_shepherd_wakeup_fast
xanim,german_shepherd_wakeup_slow
xanim,german_shepherd_sleeping
xanim,doorpeek_open_door
xanim,doorpeek_kick_door
xanim,doorpeek_jump_door
xanim,doorpeek_idle_door
xanim,doorpeek_grenade_door
xanim,doorpeek_firec_door
xanim,doorpeek_fireb_door
xanim,doorpeek_firea_door
xanim,doorpeek_deathb_door
xanim,doorpeek_deatha_door
xanim,doorpeek_close_door

This should be all but run your map in dev_script and dev on it, so u are able to update anything that was overlooked.