At a minimum, print a BASE and a TREE, black or dark green Prusament. Next, try a JACKOLANTERN, orange, with a color change to black for the face, then green for the stem. On a Prusa Mini, you can get at least 4 jackos to fit on the print bed.

The GHOSTIES are probably the simplest, just white or any other color with one color change for the face. I did have eyebrows, but the detail was too fine and they just broke off. So I decided ghosts do not have eyebrows. 

You can tell which is the CAULDRON, because of her feet. It starts with white or other light color for a background, necessary to have a place to put the notch, then black for the body plus boots, red for striped stockings plus goo, then light green for the bubbles. This is the most complex, with all the color changes.

The hat is for the Senior Woman of Hats at your party. It's just black, then yellow, finally red for the stripes.

Try more designs if you're up for it. I'm no kind of artist, but just googled “Easy draw witch hat for kids” and looked for sketching tutorials like this. After sketching, turn it into a 3D design. I've been learning OnShape, so this was a chance to practice, and keep thinking about “layers” for color changes. Other than the first layer has to be 3mm (see below), the next sections can be pretty thin, maybe two or three filament layer heights or more. I used 0.2mm layer height, with at least 3 layers to make sure the color really changed smoothly.

KEY NOTE: the whole thing is based on a half-lap concept. Each item, base, tree, decorations, are all 3mm thick at the bottom. Every piece has a 3.2mm notch in the bottom edge. This allows them to fit together fairly easily.

VARIATIONS: the base has notches on both the top and bottom edges. So, in addition to a tree, you can assemble two base pieces together at right angles (see photo) in order to make a display that does not involve a tree.

Tree hooks. The limbs of the tree have little rings. These are intended to allow hanging small pieces, like tiny jackolanterns, with string or with little Christmas ornament hooks.

SOURCE FILES: These designs are in Onshape, as a public document. Try this link to make a copy for yourself.