Adding Spikes

With the level builder open (see here), click on "Change":

Now choose "Spike Row" from the window that appears:

Click-and-drag a rectangle going upwards to make the spikes point up, or drag the rectangle down to get the spikes to point down:

Putting both together:

Health Points

The player will lose a health point every time it hits a spike.

Health points can be restored by picking up a "Health Point" pickup.

To add one choose it using "Change", and then click at the location in the game you want one to be: