I did use Ditto. Last minute substitution. ;)
He had Excadrill out against my Clefable. I thought for sure he was going to use Iron Head, so I switch in Ditto for a Not Very Effective. However, he used Earthquake and killed my poor Ditto-Excadrill. After the battle, he told me he would have used Iron Head, but his Excadrill didn't have it.