[Derision]

$client isn't exported to EVENT_TIMER.

I'm not the quest expert, but this works for me. What you can do is make a note of the name of the player who aggroed the mob in EVENT_AGGRO, then in EVENT_TIMER, lookup the Client object using the name you stored, i.e. this works:

sub EVENT_AGGRO {
        quest::emote("starts chasing after you");
        quest::settimer("countdown",8);
        $AggroOn = $name;
}

sub EVENT_TIMER {
  quest::stoptimer("countdown");
  quest::emote("lets loose a blood curdling howl(calling for help)");

  # Check if the person who aggroed us is still here
  #
  $client = $entity_list->GetClientByName($AggroOn);

  if(!$client)
  {
        return;
  }

  my $ravenous1_mob = $entity_list->GetMobByNpcTypeID(700664);
  my $ravenous2_mob = $entity_list->GetMobByNpcTypeID(700665);
  my $ravenous3_mob = $entity_list->GetMobByNpcTypeID(700666);
  my $ravenous4_mob = $entity_list->GetMobByNpcTypeID(700667);
  my $ravenous5_mob = $entity_list->GetMobByNpcTypeID(700668);
  my $ravenous6_mob = $entity_list->GetMobByNpcTypeID(700669);
  my $ravenous7_mob = $entity_list->GetMobByNpcTypeID(700670);
  my $ravenous8_mob = $entity_list->GetMobByNpcTypeID(700671);
  my $ravenous9_mob = $entity_list->GetMobByNpcTypeID(700672);
  my $ravenous10_mob = $entity_list->GetMobByNpcTypeID(700673);
  my $ravenous11_mob = $entity_list->GetMobByNpcTypeID(700674);
  my $ravenous12_mob = $entity_list->GetMobByNpcTypeID(700675);
  my $ravenous13_mob = $entity_list->GetMobByNpcTypeID(700676);
  my $ravenous14_mob = $entity_list->GetMobByNpcTypeID(700677);
  my $ravenous15_mob = $entity_list->GetMobByNpcTypeID(700678);
  my $ravenous16_mob = $entity_list->GetMobByNpcTypeID(700679);
  my $ravenous17_mob = $entity_list->GetMobByNpcTypeID(700680);
  my $ravenous18_mob = $entity_list->GetMobByNpcTypeID(700681);
  my $ravenous19_mob = $entity_list->GetMobByNpcTypeID(700682);
  my $ravenous20_mob = $entity_list->GetMobByNpcTypeID(700683);

  if ($ravenous1_mob) {
    my $ravenous1_mobnpc = $ravenous1_mob->CastToNPC();
    $ravenous1_mob->AddToHateList($client, 1);
  }
  if ($ravenous2_mob) {
    my $ravenous2_mobnpc = $ravenous2_mob->CastToNPC();
    $ravenous2_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous3_mob) {
    my $ravenous3_mobnpc = $ravenous3_mob->CastToNPC();
    $ravenous3_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous4_mob) {
    my $ravenous4_mobnpc = $ravenous4_mob->CastToNPC();
    $ravenous4_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous5_mob) {
    my $ravenous5_mobnpc = $ravenous5_mob->CastToNPC();
    $ravenous5_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous6_mob) {
    my $ravenous6_mobnpc = $ravenous6_mob->CastToNPC();
    $ravenous6_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous7_mob) {
    my $ravenous7_mobnpc = $ravenous7_mob->CastToNPC();
    $ravenous7_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous8_mob) {
    my $ravenous8_mobnpc = $ravenous8_mob->CastToNPC();
    $ravenous8_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous9_mob) {
    my $ravenous9_mobnpc = $ravenous9_mob->CastToNPC();
    $ravenous9_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous10_mob) {
    my $ravenous10_mobnpc = $ravenous10_mob->CastToNPC();
    $ravenous10_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous11_mob) {
    my $ravenous11_mobnpc = $ravenous11_mob->CastToNPC();
    $ravenous11_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous12_mob) {
    my $ravenous12_mobnpc = $ravenous12_mob->CastToNPC();
    $ravenous12_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous13_mob) {
    my $ravenous13_mobnpc = $ravenous13_mob->CastToNPC();
    $ravenous13_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous14_mob) {
    my $ravenous14_mobnpc = $ravenous14_mob->CastToNPC();
    $ravenous14_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous15_mob) {
    my $ravenous15_mobnpc = $ravenous15_mob->CastToNPC();
    $ravenous15_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous16_mob) {
    my $ravenous16_mobnpc = $ravenous16_mob->CastToNPC();
    $ravenous16_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous17_mob) {
    my $ravenous17_mobnpc = $ravenous17_mob->CastToNPC();
    $ravenous17_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous18_mob) {
    my $ravenous18_mobnpc = $ravenous18_mob->CastToNPC();
    $ravenous18_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous19_mob) {
    my $ravenous19_mobnpc = $ravenous19_mob->CastToNPC();
    $ravenous19_mobnpc->AddToHateList($client, 1);
  }
  if ($ravenous20_mob) {
    my $ravenous20_mobnpc = $ravenous20_mob->CastToNPC();
    $ravenous20_mobnpc->AddToHateList($client, 1);
  }
}

I'm sure one of the resident quest experts will chime in if there is a better way to do it.