<?php
$string = 'Call a group of 8 Shadow Beasts to plummet from the sky at a targeted location dealing 3200% total weapon damage over 5 seconds and stunning enemies hit for 2 seconds.';
echo preg_replace("/[0-9]*%/", '<span class="d3-text-green">$i</span>', $string);
Call a group of 8 Shadow Beasts to plummet from the sky at a targeted location dealing <span class="d3-text-green">$i</span> total weapon damage over 5 seconds and stunning enemies hit for 2 seconds.