PlaySoundAtEntity needs .snt, yes, but the rest should work anyhow.
Try this
////////////////////////////
// Run first time starting map
void OnStart()
{
AddEntityCollideCallback("Player", "MonsterDoor", "CollidePlayerWithMonsterDoor", true, 1);
}
void CollidePlayerWithMonsterDoor (string &in asParent, string &in asChild, int alState)
{
SetEntityActive("ScaryDude", true);
ShowEnemyPlayerPosition(''ScaryDude'');
FadeRadialBlurTo(1.0f, 1.0f);
PlaySoundAtEntity(''MonsterDoor'', ''react_scare6.ogg'', ''Player'', 0.0f, true);
}
////////////////////////////
// Run when entering map
void OnEnter()
{
}
////////////////////////////
// Run when leaving map
void OnLeave()
{
}
If that's not working, double-check that you have matching names in your code and map.