[trevius]

This would be pretty simple just using the new quest commands.

Create your sneaking NPC as race 240 and I think gender 0. Then run this script:

sub EVENT_AGGRO {

  quest::npcrace(433);
  quest::npcgender(2);
  quest::say("DIE!");

}

That should do what you want. Though, I am sure you could customize it and add more wherever you like.