Introduction: Cauldron of Cthulu - Moving Tentacle Prop

About: Hands-on DIY lover and borderline crazy crafter. I love Halloween and creepy food.

A few years ago I made 'Cleopatra,' an overly complicated, incredibly time-consuming moving plant animatronic that I absolutely loved, but also hated simply because she took so much time to create.

This year I wanted something with just as much impact, but in a brighter, more cartoony style that would take a fraction of the time. Thus the Cauldron of Cthulu was born.

And because I believe in giving credit where credit is due, this project was inspired in no small part by the amazing box of snakes by Saul Films (check him out...his stuff is AMAZING!)

While I wanted something similar, I wanted to put my own specific spin on it...


1 giant plastic cauldron (the bigger the better)

1 can spray foam

1 can electric green spray paint

1 can glow in the dark spray paint

1 electric neck massager (can usually find on Ebay or on Facebook Marketplaces for super cheap)

3-4 pool noodles (depending on how many tentacles you want to make)

1-yard purple lycra spandex

1/2 yard green lycra spandex

clear suction cups in varying sizes (I bought 3 bags of these for a total of 60)

6-8 6" lengths of 1/2" PVC pipe (again, depending on how many tentacles you want to make)

1-3/8 in. x 36 in. Zinc-Plated Punch Flat Bar cut into 6" strips

2 steel hose clamps

Mini bungee cords

Polyfil stuffing


Glue gun and glue







Step 1: Prepping Your Cauldron

The first thing you want to do is get your cauldron ready. I started by first drilling a hole in the back approximately 1" around so I could feed the power cord of my neck massager through later.

Next, I used my spray foam to give it a proper drippy look.

WORD OF WARNING: Make sure you don't let the spray foam drip too far into the inside of your cauldron. I went overboard and as a result, couldn't fit all my tentacles in how I wanted as they kept scraping against them (I discuss this later on and you can see how it turned out at the end of this tutorial). Word to the wise, keep the spray foam only on the outside edge of your cauldron and leave the inside edge clean.

I coated the spray foam with a good blast of electric green spray paint and followed that up with some glow in the dark paint so it would pop under the blacklight.

Set the cauldron aside for now. We will come back to it later.

Step 2: Making the Structure of Your Tentacles

To make your tentacles 'wavy' you will have to first prep your pool noodles and make them 'springy' by spiral cutting them.

First cut your noodles in half. Then, using your knife, carefully cut down the length of your noodles in a spiral motion, making sure not to cut all the way through. For springier noodles, make your spiral tighter. For stiffer noodles, make the spiral wider. I found the sweet spot was spiraling down in a 2" wide cut.

To create varying levels of wave, try alternating your noodles with different widths of spirals.

This is an optional step and if you decide not to spiral cut them, your tentacles will be much stiffer and instead of flopping around, will simply wave back and forth.

Step 3: Skinning Your Tentacles

Take your spandex and cut out a piece of green (the belly of your tentacle) and purple (the back of your tentacle). For the back, I cut a piece 3 feet long and 3 inches wide.

For the belly, I did a strip 3 feet long and 2 inches wide. Taper the ends to make the tip of your tentacle and sew together wrong side out all around the fabric, leaving the bottom open.

Turn right side out and stuff the ends with about 4" of polyfil. This will give your tentacle a bit of weight at the end and help assist in the waving.

Stuff your spiral cut pool noodle into your tentacle 'sock'. You will have some material left over at the bottom. Simply fold this up inside the hollow part of your noodle and jam it in there. We'll glue it into place in a little bit.

Now let's add our suckers!

The bag of suckers I got had three different sizes. I started at the top of my tentacle with the smallest size and moved my way down, getting gradually larger. To attach them, place a generous blob of hot glue onto your tentacle and then press your sucker into the hot glue. You'll notice the hot glue actually melts the pool noodle behind the lycra, making your suckers really 'embed' into the material. This will help hold them.

Continue adding suckers until you have your tentacle covered.

Step 4: Assembling the Bones of Your Tentacles

For this step, you'll need your PVC pipe and your flat punch bar. Each should be about 6" long.

Using screws, attach the punch bar to the bottom of your PVC pipe at about 2" as show in the photos here. You want the pipe to extend up from the bars.

Once you get all your bars attached, take the PVC end of your pipe and slide it inside your tentacle at the base where we previously stuffed the fabric.

Secure tightly with lots and lots of hot glue. No, really, use more. They'll be waving around, you want them to be as secure as possible.

Step 5: Assembling Cthulu

Carefully disassemble your neck massager by removing the front padded cover over the massaging knobs. This can be done either by unscrewing the unit and removing the piece or by simply cutting the fabric away. Either way, you want to expose the two rotating knobs.

Using your pipe clamps, secure the plate ends of your tentacles to the knobs. Tighten them TIGHTLY. As they move, they'll have a tendency to loosen, so the tighter they are, the less likely you are to have a tentacle come flying off at you later.

The knobs will want to rotate which looks weird when you have the unit turned on. To help keep them in place, use a few of your bungee cords to secure the rotating knobs to the side of the massager unit. The bungee cords won't inhibit the movement of the kneading arm, but they will keep the tentacles from spinning.

Attach all your tentacles to your massager.

Follow up to the spray foam note: While I had originally wanted to have all six of my tentacles waving, I discovered I couldn't get them to wave as much as I wanted because I had gone overly crazy with my spray foam. I ended up having four waving and used screws to attach the last two to the inside of the cauldron.

Step 6: Finished! Step Back and Enjoy!

Carefully place your massager and tentacle monstrosity into your cauldron. Feed the cord out the back and plug it in. Step back and enjoy your ridiculously simple and yet really effective Cauldron of Cthulu! For maximum effect, place near a blacklight to really enjoy how the colors pop (and the clear suckers automatically give off an eerie blue glow which is so cool too!)

A note: The unit does make a bit of noise, so to really sell the effect, I actually played sounds over the speakers in my yard with lots of creepy swamp sounds and it helped a ton.

Happy haunting!!!

Halloween Contest

Runner Up in the
Halloween Contest