They created the ball game. They were so good at it that they became enemies with the Lords of Death. They got mad because of the noise.
The Lords of Death called them to the Underworld, and Hunahpu, one of the twins plucked a piece of his hair and made it a mosquito to spy on the Lords. They successfully passed the first two tests.
One of the many tests the twins had to go through was walking into a house with nothing but a fire, they were not burned, but merely just toasted or simmered. This left the Lords extremely stumped.
They kept on tricking the Lords, and they knew they could not do this forever, so they ran. Knowing that they would be reborn, they found a cliff and jumped to their death.
When they became reborn, the Lords wanted to experience that too, so the Hero Twins sacrificed two of the Lords, but never revived them. The remaining Lords of Death then became afraid of the twins Because they had realized that these were no ordinary twins. They were the Hero Twins. This is how they defeated Xibalba.