My brother got an American bulldog / lab mix puppy from the local pound. At least that's what we think she is. Her name is Lucy. She's about 4 months old and she's a bag of muscle. Absolutely fearless. She constantly tries to play with my mom's 12 year old cockapoo, and despite the cockapoo's snarling and snapping, Lucy sticks her face right in the cockapoos face and tries to play.
She seems to heed commands alright, but she can be stubborn. And when she gets playing rough, she'll tear you up. She's only 30 lbs but I was running with her in the yard, kind of playing keep-away, and I heard this snarl from behind me. I turned around to see her flying through the air and she grabbed my arm with her puppy teeth. She was playing, but still intimidating.
Sorry no pics right now. I'll try to get some.