How do I script this?

[ApeCake]

Use AddEntityCollideCallback and timers. The script would look like this:

void OnStart()
{
AddEntityCollideCallback("Player", "nameofScriptArea", "spawnmonster", true, 1);
}

void spawnmonster(string &in asParent, string &in asChild, int alState)

{
SetEntityActive("Nameofmonster", true);
AddEnemyPatrolNode("Nameofmonster", "PathNodeArea_1", 0, "");

AddTimer("playsound", 10, "PlaySound");
}

void PlaySound(string &in asTimer)

{
//play sound here, use either PlayGuiSound or PlaySoundAtEntity, example below.
PlaySoundAtEntity("","react_breath_slow.snt", "Player", 0, false);
AddTimer("startcredits", 20, "StartCredits");
}

void StartCredits(string &in asTimer)

{
StartCredits("creditsmusic.ogg", true, "Ending", "MainCredits", 1337);
}

I'm fairly sure that should work.