DownloadStarsMap.user.js

// ==UserScript==
// @name         DownloadStarsMap
// @namespace    http://tampermonkey.net/
// @version      1.0
// @description  try to take over the world!
// @author       You
// @match        https://strellas.com/kreator/*
// @grant        none
// @require http://code.jquery.com/jquery-3.4.1.min.js
// ==/UserScript==

(function() {
    'use strict';

    $('.poster-options .poster-container').first().prepend(`<a class="downloadStarsMap" href="#">Descargar Mapa</a>`)
    $('.downloadStarsMap').on('click',function(e) {
        e.preventDefault(); //stop the browser from following
        window.location.href = $(".img-responsive.stars-map").first().attr("src");
    });
})();