Does the tournament not count?

[shogun00]

It must be done in single player mode (regular or classic) and you don't need to hit the exit for it to pop. You do need to take out the spiders quickly though (20 seconds iirc).

[BennyJackdaw]

Just I had killed all the spiders in The Sorcerer's Lair arachnid attack challenge, twice even, but neither time I got the achievement for it. The first time I can sort of understand because I did not make it to the exit ramp and I also wasn't online at the time, but the second time I managed to do it and hit the exit ramp while playing a tournament online, and I STILL didn't get the achievement. So, wait, tournaments don't count? I can still power up my upgrades, so why don't I got the ability to unlock achievements while playing in a tournament. Also, this was without wizard mode power-ups by the way.