At a Con a few years back, right after 3.5 came out, I was signed up for a game last session of a Saturday, showed up, there were 13 other players there (me and my buddy signed up together) to find out that the DM/Constafff had some confusion on registration. It was supposed to be 1 long all day event, however in the reg book it showed up as the same, repeating 3 times. The DM decided to allow those who signed up to just keep staying from the earlier sessions, and the later, to jump in, and, he simply Tport'd us in for simplicity sake as 'reinforcements', and he had pregens, but ran out of course, so whoila, I get 40 minutes to roll up a level 18 human wizard, fully geared. Talk about turbo....

SO, to the point, 15 PCs and it was all about some undead, so to scale it he just added more lesser vampires, wraiths, giant zombies/skels etc....

15 PCs, vs about 100 or so various mid to high level undead all in a large open cavern. The battle was just starting at beginning of session. It took less than 20 minutes. And most of the time was me explaining why they were all destroyed.

The DM had only 1 pregen caster, a sorc. No one else who had to make a character, made an arcane. So knowing what we were going into, I planned for it, used item creation feats, etc... made lots of items to max, empower, enlarge, widen, twin and repeat spells. Time Stopped on my 1st initiative, set it all up. Whoila. Needless to say the DM wasn't pleased, but he wasn't that bright either, obviously had never dealt with a player of arcane magic at high levels.

The only thing he flat out refused me, was to Gate in anything. Which there was no reason why, other than "cuz I said so..." So Time Stop and battle field shaping, buffing, and 1 round, and the DM had the BBEG Tport away, just cuz he didn't like it. The BBEG was a level 20 Vamp (human) wizard. But he figured out right quick, a couple max'd fireballs weren't all that cool against 15 buffed PCs