Mutations - trying to solve using regex

I need a hand with this problem, I’ve solved all requirements except for the first and the second last one using regex:

function mutation(arr) {
  var str = /[:alpha:]+/gi;
  return str.test(arr);

mutation(["hello", "Hello"]);

I’m new to using regex and wondering if there are extra expressions that I could be adding to clean up the outstanding requirements?

I’m actually surprised that works at all as I didn’t think POSIX style character classes were read in the JavaScript regex engine. You can spend a lot of time learning regex at regexr, which includes a handy guide to special characters on the left. I don’t think regular expressions will work for this problem, though. You’ll get some answers right (maybe pass the challenge), but it would be luck. What happens if you had to compare “lelhlo” and “Hello”?

Also, I cleaned up your code and added spoiler tags.
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