It's a once per week game. We would alternate characters each week. I was warned that eventually, my evil character would be taken from my hands and would revert to the DM's control.
That time came a while back, but I never felt the repercussions of it with my main, heroic character until the last time I played. I created a monster. The villainess I'd created, which my main character had never even heard of until last session, has become my worst nightmare. I've created a villain I can't defeat. I've screwed myself over. And I didn't even realize what I'd done in the beginning, I'd never thought of her as so unbeatable.
After a very brief, disastrous confrontation, ending with my heroine being captured, imprisoned and interrogated and tormented for weeks before being rescued, my villain has become my heroine's worst nightmare.
My DM is quite pleased.