holy freaking cow, no wonder it lags....it looks like in the EC it spawns a bunch of animated billboard particles, lol, CC it's just a simple ring "burst" animation (which imho actually looks pretty cool), if done properly in the engine the EC is using they could make a higher res version of that same effect which would look pretty awesome and would be only a few primitives so it wouldn't cause much overhead at all. As a matter of fact, they could do the effect it's doing now but BETTER with a simple fire shader, and instead of spawning a gazillion seperate sprites just spawn a simple mesh that expands. (I actually did an effect very similar to this in one of my UT2004 mods way back that had a huge circular blast around the impact point, and it ran without causing lag on cheap video cards in 2005). From looking at the video of a corgul fight in EC id' hazard a guess that they didn't want to do the artwork for the attack so they simply took the explosion spell animaiton and played it hundreds of times expanding outward as a "fire ring". Talk about lazy...you'd think they weren't making money off UO with such little care shown.
I'd bet they didn't even bother to use instancing if supported as well from how it seems to lag with so few on screen even.....