I had thought it was nearly impossible during the first 100, but after 170 or so, I started to have problems. Finally caught up to me in battle 199.
946 Latias is the lead, and two DM's are all it takes to KO Spiritomb, but I managed to Trick the Scarf, and I used Articuno to KO. Then 780 Foretress comes out. I switch to Swampert, the damn thing explodes. I switch Articuno back in, and what should come out but 851 Aerodactyl? One Stone Edge, and I'm done. That was ridiculous.