Simple script that plays Kill the King automagically. https://codepen.io/jcoulterdesign/full/MWeZWxQ

Kill-The-King-Beat-Script.js

document.querySelector('div.game_intro__inner.start > p').click();
setTimeout(() => {
    document.querySelector('div.game_intro__inner.end > div > p.continue').click();
    var lastXp = 0;

    function loop() {
        var stage = parseInt(document.querySelector('div.ui > div > div.ui_progress__stage').innerText.slice(6));

        try {
            var xp = parseInt(document.querySelector('div.game_inner__footer > div.resources > div').innerText.replace('xp', ''));

            for (var idx = 1; idx <= 3; idx++) document.querySelector(`div.upgrades > div:nth-child(${idx}) > div`).click();

            if (lastXp <= 0) document.querySelector('div.nextPhase').click();

            lastXp = xp;
        } catch {
            document.body.onkeyup({ keyCode: 32 });
        }

        setTimeout(loop, stage === 9 ? 350 : 1);
    }

    loop();
}, 5000);

easy peasy lemon squeezy