Victini is quite underrated, despite being a "Mew-esque Event". Meloetta is quite underrated as well, despite being an Event Legendary. Bunnelby is quite underrated but it can have the ability Pickup. Plus it can learn a variety of moves.
I see it's best to have something to counter Gliscor's main weakness to Ice. I still say the best Gliscor to use is the one that has poison heal. I consider Gliscor my fav Gen 4 Pokemon even though it evolves from a Gen 2 Pokemon.
Yeah, that weakness to ice really wrecks the strategy for him. I always enjoy putting I nice fire type sometimes or steel to resist all those ice moves ^^ like a heatran sometimes, though not very useful against mamoswine XD
Thing was, I underestimated Ice-Types by then, and only had one Dragon-Type (which only had the Dragon TM moves I taught it.)
I never really knew about type advantages back then. I knew the simple ones, like Grass beats Water and Water bears Fire and after battling learned a few more (Psycic beats Poision.) I now know how to simply use another Dragon-Type from Dragonspiral Tower.
I did have Reshriam, but he was only level 50, and since Dragon beats Dragon, he was down pretty quickly.