recover monster thrash numbers and hidden town flags in valleydy

rsrc/scenarios/valleydy/towns/town20.xml

@@ -8,7 +8,10 @@
     <bounds top="0" left="0" bottom="28" right="31" />
     <difficulty>3</difficulty>
     <lighting>dark</lighting>
-    <flags />
+    <flags>
+        <chop kills="2" />
+        <hidden>true</hidden>
+    </flags>
     <item id="0">
         <type>222</type>
     </item>