You are playing The Binding of Isaac: Wrath of the Lamb hacked and unblocked by BlessFlasher.com.
Isaac lives alone with his mom, and they have a very happy life together. One day she hears the voice of god, telling her that Isaac is living in sin and she needs to fix that right away.
So, she takes away all of his toys and locks him in his room. That's not enough, however, and to prove her devotion, she had to perform one final task: kill Isaac. But Isaac is a clever little boy and he escapes into the basement before she can catch him. Take that, mom!
As it turns out, the basement isn't a very friendly place, and Isaac now has to deal with all sorts of nauseating abominations. He has a few weapons and power-ups to help him through it all, though. Move around with the WASD keys and fire tears (Isaac's weapon of choice) in any direction with the arrow keys. You can drop bombs with E and use a secondary item (when you obtain one) with the spacebar. There are plenty of things to pick up and lots of secrets to find in this deeply-layered basement, and you'll need every trick you've got to survive.