So, I've got this party of 11th level bad-asses, and I've been trying to figure out how to inflict massive amounts of pain upon them. Several of them have insane armor classes (like 33 when buffed) and so trying to hit that is difficult.
So, I was thinking about shadows. Shadows only need a touch attack, and their strength drain attack is nasty, nasty. So, I was thinking, "wow, wouldn't it be scary for them to explore this ancient dungeon and come across a room full of shadows."
And then reality set in - that's a few rounds away from a TPK, dumbass! Because you can't stop a shadow! With a normal creature, you can throw up a wall of force (a favorite tactic among the party's sorcerer) and block them off, but a shadow can just seep into the ground or ceiling and come up right below you. Which is cool for me, but if one of the players gets hit like more than 3 times by a shadow the player is looking at insta-death, which is not cool for them.
By the same token, the party has access to area effect spells like fireball, so they could empty out a room of shadows, and the cleric has greater turning, so he could get rid of a fair amount easily as well.
So, I was thinking that I could have them come in waves and waves. The first few waves would be dispatched easily, and then as they use more and more resources getting rid of them using AE spells and turn undead checks, once they run out of those, then they have to deal with them one-on-one, and then that could be scary.
So, how many shadows would be a reasonable number for me to throw at a party like this such that when they are done, everyone in the party has a single-digit strength, and no spells, and no turn undeads left.

It would be cool if it got the point where the sorcerer had to resort to beating at the shadows with a stick because he was tapped out.
The problem, of course, is that if anyone goes to 0 str, they become a shadow in 1d4 rounds, and that's not cool. So, I want to avoid that if possible.