Game_Enemy.prototype.refresh = function(){
    Game_BattlerBase.prototype.refresh.call(this);
    if (this.hp === 0) {
        this.addState(this.deathStateId());
        $gameParty.enemyKills[this.enemyId()] = ($gameParty.enemyKills[this.enemyId()] === undefined) ? 1 : $gameParty.enemyKills[this.enemyId()] + 1;
    } else {
        this.removeState(this.deathStateId());
    }
};

var _prt_alias = Game_party.prototype.initialize;
Game_party.prototype.initialize = function(){
    _prt_alias.call(this);
    this.enemyKills = [];
};