<event>
  <action>
    <entry if_timer="DespawnTimer" action="a1+a2"/>
  </action>
  <linked_action name="a1" action="log" message="Mobs despawned by timer"/>
  <linked_action name="a2" if_area="electro" if_area_count="0" if_area_count_mob="player" action="remove" sub="mob" target="all_mobs_in_area" target_area="electro"/>
</event>