Verify that all characters in second array element are contained in first element.

mutations.js

function mutation(arr) {
    var str1 = arr.slice(0, 1).join(" ").toLowerCase(), 
        str2 = arr.slice(1).join(" ").toLowerCase(),
        hits = 0;
    for (var i = 0; i < str2.length; i++) {
        if (str1.indexOf(str2[i]) !== -1) {
            hits += 1;            
        }
    }
    if (hits === str2.length) {
        return true;
    } else {
        return false;
    }
}

mutation(["Alien", "line"]);