How can you translate this into Regex: Replace any char (aka '.') that is repeating more than once and replace it with one of that char with the exception of "ii" and "iii".
$reg = preg_replace('/(.)/1{1,}/','', $string);
Now this must replace VVVVV with V or .... with . and must not replace Criiid (or Criid) but Criiiiiiid with Crid.
Feel free to comment if you don't understand the question.
preg_replace('/([^i])\1+|(i){4,}/', '\1\2', $string)
Note that this will squeeze everything -- spaces, newlines, etc.
The first alternative replaces anything but i, the second alternative replaces any is which occur four times or more:
$reg = preg_replace('/([^i])\1{1,}|(i){4,}/','\1\2', $string);
Or (thanks to @Enissay):
$reg = preg_replace('/([^i])\1+|(i){4,}/','\1\2', $string);