Code for Thomas Chessa McSnake

array_stuff.php

<?php
$bucketOne = ['yellow', 'red', 'blue'];
$bucketTwo = ['yellow', 'yellow', 'red', 'blue', 'blue'];

//filter the second array so that there are only duplicated values in there
$values = array_filter(array_count_values($bucketTwo),function ($value) {
    // > one means in the bucket it must appear at least 2 times, you can check for `$value == 2` if you only what elemnts that apprears twice and not more
    if ($value > 1) {
        return $value;
    }
});

//remove all arrays from bucket one those ar not in the filtered bucketTwo
$output = array_intersect($bucketOne,array_keys($values));

var_dump($output);