Agent P, aka Perry the Platypus Birthday Cake

Print Friendly

Andrea Meyers - Agent P, aka Perry the Platypus Birthday Cake

Follow Me on Pinterest

My husband Michael, the engineer, is the designer for all our sons’ birthday cakes. He’s a big fan of Cake Boss and Ace of Cakes and tries to pick up tips when he watches the shows. We only tackle cakes like this three times a year and we are definitely not pros. I bake the cakes, whip up the frosting and fondant and marshmallow treats, and he does all the assembly and decorative work. Here’s our story on how we made the Agent P birthday cake.

When we first watched Phineas and Ferb with our boys a couple years ago, we knew it was just a matter of time before one of them requested a birthday cake for one of the characters. For Halloween 2009, Builder Guy wore a homemade Agent P aka Perry the Platypus costume and everyone thought he was an off-colored beaver. When he reprised the costume this last Halloween everyone knew who he was, many times singing, “Doo-be doo-be doo-ba, doo-be doo-be doo-ba. Agent P!” So it was no big surprise when he asked for an Agent P cake.


Andrea Meyers - Agent P

Agent P has a couple key features that we needed to perfect: the eyes, the platypus bill, the tail, and the secret agent hat.

Andrea Meyers - Agent P cake plans

One of the great things about Agent P is he’s always disappearing through trap doors to his secret lair, and one of his exits is through the lawn, so that is what we attempted to recreate here.

Michael played with the design of Agent P for several months. His thin vertical body wouldn’t yield much cake and the rim of the hat was a challenge. Getting Perry right size was also key. The action figure was about one inch wide and four inches tall. We decided to scale him up, one inch of action figure equal to four inches of birthday platypus. The dimensions were so problematic we decided to make him out of marshmallow treats. We added extra cereal to the treats so they would harden up and be more structurally sound, though not really edible unless you wanted a sore jaw.

Andrea Meyers - Agent P assembly

The orange bill of our model really stuck out there and initially this was our biggest challenge. After a bit of trial and error we trimmed down four chopsticks and embedded them in the bill through the body, and it worked, after adding a thin layer of treats on the underside of the bill to help stabilize it. In this case it helps to make marshmallow treat sculptures a day or so ahead before frosting them to give the piece a chance to harden up.

When Michael made the eyes it made the sculpture resemble Homer Simpson than Agent P, so he trimmed the eyes down using the model as a guide and got them right. Fortunately the action figure’s brown Stetson came off so that helped us get a good look at the eyes and an accurate measure of the hat. He had planned to make the hat brim out of a flour tortilla, but for our Perry the scale was not right. Fortunately we had some 8-inch flat bread on hand, and that seemed to scale out right. Michael warmed it on a cast iron skillet, shaped it, then let it stay out overnight.

Frosting Notes

Below are the frosting quantities, which may vary slightly depending on how thick you apply it. You can make extra frosting and have leftovers for other uses, or you can start with the quantities listed and make more if needed. If you make two full batches of vanilla buttercream you should have just enough. We find using Wilton frosting gel colors help keep the colors consistent if you have to make another batch. Colors do tend to darken after resting a day.

Plan Ahead

  • Bake the cake up to one day before and allow it to cool completely. Freezing it for about 30 minutes before assembly makes it easier to carve, although on this project the cake carving is minimal.
  • Make the frosting up to three days before. Cover the surface with plastic wrap and store in the refrigerator. Allow to come to room temperature before frosting the cake.
  • Make the marshmallow treats and the Agent P sculptures a day ahead. Letting the sculpture dry out a little overnight helps make frosting it a little easier.


  • We strongly recommend adding extra cereal to the marshmallow treats to make them sturdier, though if you really want you could carve Agent P out of green florist foam and then apply the frosting.
  • Because the hat is top heavy, we recommend doing the finally assembly in place. Don’t try to put it all together in the kitchen then carry it half way across the house with candles lit, because the hat may topple off.

Our Thoughts on Fondant

You can use fondant for the cake rather than buttercream, either purchased or homemade. Zoe of Zoe Bakes (one of my favorite bakers) has a tried and true recipe for homemade fondant or you can purchase premade fondant. Michaels craft stores now sell a Duff branded fondant that we’ve heard is pretty good, even edible, though it’s rather pricey. Fondant gives the cake a professional-looking, sleek, smooth surface, but no one in our family will eat it and that’s why we skip it. Wet paper towel can also be used to smooth out the final coat of buttercream, though it probably won’t be as smooth as rolled fondant.


Serves 30 to 40.


Agent P toy or photo
11” x 15” x 2” cake pan, greased with a layer of parchment in the bottom
stand mixer with paddle attachment (or hand mixer and large bowl)
wax paper or silicone mat
32-ounce yogurt or cottage cheese container with lid (about 4-1/2 inches across)
4 (8-inch) chopsticks
13” x 19” cake board, covered with foil
corrugated cardboard square, approximately 7” x 7”, covered with foil
3 #3 piping tips + coupler
1 #16 star tip + coupler
4 quart-sized freezer bags (for piping frosting)
angled frosting spatula
popsicle sticks (for portioning gel colors)
green florist foam (optional)


2 batches chocolate cake, yellow cake, or other cake of your choice
2 batches vanilla frosting, no shortening OR
2 batches vanilla frosting, with shortening (We only use shortening when the weather is really hot and humid.)
1 batch chocolate frosting
teal frosting gel color
leaf green frosting gel color
orange frosting gel color
black frosting gel color
3 batches marshmallow treats (Add 2 extra cups of cereal per batch.)
8-inch piece of pita bread

Make Ahead

1. FROSTING – Make both batches of the vanilla frosting. Reserve 1/4 cup for white. Tint 2-3/4 cups leaf green. Tint 1-1/4 cups orange. Tint 1-3/4 cups teal.  Make the chocolate frosting. Tint 1/4 cup dark brown using a touch of black. The color improves while sitting, so you can make this a day or two ahead of time. Refrigerate if making ahead.

2. PERRY HAT – Lightly toast an 8 to 9-inch piece of pita or other flatbread. While it’s warm, gently shape the bread to form the rim of the fedora hat, curled up in the back and slightly down in the front. You can prop the back edge on an oven mitt to help keep its shape while it cools overnight. Using the yogurt container lid as a pattern, cut 3 rounds of the marshmallow treats and stack them on top of each other, compressing with your hands. Cut two small triangles and shape them for the front and back of the hat, and place on top of the stacked marshmallow treats.

3. PLATYPUS BODY – Cut 6 more rounds of marshmallow treats. Stack 4 on top of each other and press them together. Cut a 4” x 8-1/2” rectangle of marshmallow treats and trim the corners, then round them using your hands.  Press the 4 chopsticks lengthwise across the beak, trimming the ends as necessary. Use some of the marshmallow treat trimmings to build up over the ends of the chopsticks at the front edge of the beak. Turn the beak back over and place it on top of the body. Stack the remaining 2 rounds of marshmallow treats on top of the beak, pressing them together. Use some of the trimmings to mold the ridge in the middle of the beak and the bump outs on the sides of the beak. Use the other trimmings to mold the eyes.

Andrea Meyers - Agent P sculpture

4. PLATYPUS TAIL – Cut a 6” x 4” rectangle of marshmallow treats, then shave the long sides so it tapers down to 3” at the bottom.


1. AGENT P – Using the angled spatula, spread a crumb layer of the teal frosting over the body and back and top of the head. Use the orange frosting to put on a crumb layer over and under the beak. Allow to dry. Finish the body with the final layer of teal frosting and the beak with the final layer of orange frosting. Spread on the white frosting for the eyes, then using #3 tips, pipe on some chocolate frosting for the eyes and a finishing edge of teal around the eyes.

Andrea Meyers - Agent P sculpture, decorated

2. HAT – Use the angled spatula to spread on a crumb layer of the chocolate frosting on the top and under the rim of the hat , then set it on an inverted yogurt or cottage cheese container and allow it to dry. Spread on the final layer of chocolate frosting and use the dark frosting to spread the band around the hat. Using a #3 tip, pipe more dark chocolate around the edges of the band.

Andrea Meyers - Agent P hat, decorated

3. TAIL – Using the angled spatula, spread a crumb layer of orange frosting on both sides and around the edges of the tail. Allow to dry, then spread on the final layer of orange. Use the edge of a knife to draw a cross-hatch pattern on the top side of the tail.

4. CAKE – Use the foil-covered square piece of cardboard as a pattern to cut out a square of cake from one side, then place the cutout on the cardboard square. Spread the leaf green frosting around the outside edge of the base cake and the chocolate frosting around the inside of the cut area and around the outside edges of the cutout. Use the #16 tip to pipe stars all over the top of the base cake and the cutout cake. (Note: At the time we incorrectly estimated the amount of frosting required and had to leave a bare space that would go under the cutout, but the recipe has been written to have enough frosting.)

Andrea Meyers - Agent P birthday cake base


1. Place Agent P inside the cutout area of the base cake. Place the tail inside the cutout area with the narrow side propped against the platypus body and the rest laying over the cake. It may bend slightly and that’s ok.

2. Place the hat on top of the the platypus head with the curled brim in the back. Make sure it’s low over the eyes.

3. Place the cutout piece of cake on top of the base cake off to the side and a little angled.

360° VIEWS

Andrea Meyers - Agent P, aka Perry the Platypus Birthday Cake

Andrea Meyers - Agent P, aka Perry the Platypus Birthday Cake

Andrea Meyers - Agent P, aka Perry the Platypus Birthday Cake

More Birthday Cakes for Kids

Andrea Meyers - Airplane Birthday Cake Andrea Meyers - Little Einstein Rocket Birthday Cake Andrea Meyers - Lightning McQueen Birthday Cake

Andrea Meyers - Volcano Birthday Cake Andrea Meyers - Percy Train Birthday Cake Andrea Meyers - Toby Train Birthday Cake

Andrea Meyers - Lego Star Wars Stormtrooper Birthday Cake

[Disclosure: This blog earns a small commission through affiliate links.]


  1. says

    OK, I really don’t know who agent P is, but that cake is amazing! I wish I had the skills and patience to decorate cakes. GREAT JOB!

  2. Haley says

    I totally love this!
    My dad’s 47th birthday is this month and he’s such an Agent P fan! Lol,
    I’m deff making this for him.
    Awesome tutorial!

  3. Danny Vega says

    my nephew is a huge agent Perry fan and well i am going to attempt to make this cake for him for his bday this weekend, thanks for posting this i know he will have a kick out of it, Wish me luck!!


Leave a Reply

Your email address will not be published. Required fields are marked *