Conditions can depend on whether the attacker is the player or not. Needs more work

combat.js

@@ -98,6 +98,8 @@ function grappleDevour(attacker) {
       }
     }, requirements: [
       function(attacker, defender) { return isNormal(attacker) && isGrappled(defender); }
+    ], conditions: [
+      function(prefs, player=false) { return player || prefs.player.prey }
     ]
   };
 }

feast.js

@@ -22,7 +22,7 @@ let prefs = {
 };
 
 function filterValid(options, attacker, defender) {
-  let filtered = options.filter(option => option.conditions == undefined || option.conditions.reduce((result, test) => result && test(prefs), true));
+  let filtered = options.filter(option => option.conditions == undefined || option.conditions.reduce((result, test) => result && test(prefs, attacker === player), true));
   return filtered.filter(option => option.requirements == undefined || option.requirements.reduce((result, test) => result && test(attacker, defender), true));
 }