I have no clue how this happened... I was duoing Devegetators in Abyssea-Vunkerl and while me and my friend were killing these, during a fight my automaton casted Stoneskin on the enemy. At first I thought it was a graphical glitch, but no, the crawler received the full effect of the spell and my friend confirmed it as it appeared on his chatlog as well. This occurred on the PC version.