100 Doors Underground Stage 19 Walkthrough is shown below with screenshots. The answer for this level is explained in detail in the text. Look at the screenshots for more help. If you only want to look at part of the guide and not cheat, just look at part of the solution. This will help you go to the next level.
1. Pick up the knife and use it to cut the string on the balloon.
2. Use two fingers on one hand to drag the spike block to the balloon to pop it. Pick up the key and use it on the door.