Beneath the Fratelli's hideout lies a large basement with sewer pipes and heat vents which give off big jets of flame. More rats abound in the depths, but now both Fratelli brothers are on to you, and Mama Fratelli has order your capture. You'll need to wander into the back rooms to find all of the keys.
In addition to rats, the singing Fratelli joins his brother in the attempt to hunt you down. If you collected the headphones from Stage 1, you have little to fear from him other than physical collision. The flame jets the blast over your head are only a threat if you did not collect the flamesuit in the last stage. If you didn't, you will have a chance to collect one here as well.
You start out on the right side of part A. Skull mouth C nearby takes you to the exit of the stage, which does you little good if you haven't collected the keys yet, so save it for last. Instead, move left towards skull mouth A. Save the isolated skull door that sits in a small chamber for later (it may turn out that you don't need to open it at all.) Open up the two high skull doors as you make your way left, and open the left most skull door on the bottom floor, and proceed through skull mouth A.
You'll end up in the left side of part B, the darker back side of the basement. There's one diamond for you to collect here if you bother to search the upper platform. Make your way down to the bottom and climb down ladder B to part C. Proceed left and open the two skull doors that you encounter along the way. When you reach the end, if you haven't collected three keys and a Goonie by now, you'll want to investigate the skull door that's all the way to the right on the bottom level. Make your way back to ladder B, up to part B, and back through skull mouth A.
Back in part A, return to the right. If you still haven't collected the necessary items to escape (or if you're just curious), make your way to the lower level on the right, and climb up the ladder to open the skull door in the isolated chamber (watch out for rats.) Once you've collected everything, proceed through skull mouth C to the right side of part B. Navigate the ladders to reach the lock at the end of the level, and exit the stage.
There are four skull doors in this section, and three more in part C. As a result, you may find some other useful items besides keys and a Goonie, such as a Red Potion or a Slingshot. Don't be so quick to grab the potions if you have a full health meter. Try to save them until you take some damage.
If you did not pick this handy fire protection up in Stage 1 you have the opportunity to collect one here. Reveal an item bag that lies immediately to the left of the skull door in part A that lies to the east of skull mouth A. You'll need it in order to pass under the flame jets without fear.
The value of this item cannot be underestimated. There are more water-based traps than any other kind, and this raincoat will prevent you from taking damage if you touch them. You must find it on the platform of part C that is immediately to the right of the left most skull door. Try not to leave this stage without it.
The original writer of the movie makes a special guest appearance in this stage. If you can reveal him and collect him, you will be awarded 5000 points. He's hidden in part C, on the floor directly above the right most skull door.