Place one Bundt cake round-side-down on a parchment lined cookie sheet for the bottom of the pumpkin. Put a layer of cinnamon buttercream on the cake. Place the other Bundt cake round-side-up on top of the frosted cake. Spread a light and even base coat of cinnamon buttercream to the outside of the the pumpkin cake and refrigerate until set, about 30 minutes.
Make a ridge of fondant to create the top of the pail by rolling out a thin rope of fondant. Place it on top of the pumpkin cake and pinch the fondant to a triangle so that it sits flush with the cake and rises to a point. Spread a second layer of buttercream frosting making sure to fill in against the fondant ridge so there is a smooth transition to create the lip of the pail. Chill for 30 minutes until set. Spread the final layer of buttercream and use your spatula to smooth out the frosting. This final frosting layer needs to be smooth so that your fondant will be smooth. Allow it to chill for another 30 minutes.
Carefully transfer the chilled cake to a clean serving platter and fill center with a bag of real candy corn, adding in 2-3 of the candy corn teeth you made. Cover the hole with the single cupcake that you made and frost the top with the remaining frosting. Chill another 30 minutes or overnight.
Roll out your orange fondant into a 30-inch long by 6-inch rectangle that is about ⅛-inch thickness. Wrap the outside face of the pumpkin with the fondant allowing the ends to overlap in the back or side of the pumpkin cake. Cut through overlapping fondant pieces to create a clean edge by removing the cut ends so that the ends seam together perfectly. Smooth out fondant to seal seam. The top will still be unwrapped at this point, but trim bottom of fondant and tuck into the bottom of the cake and smooth out any imperfections. Roll out a 10-inch circle and place on top of the cake, trim and smooth out. Pinch the top seam, it's okay if it isn't perfect, the pail is supposed to look old and worn. (Sorry I didn't get any pictures of this step...it was my first time working with fondant, so I was too nervous about what I was doing to think to take pictures.) Create a template (I printed out an enlarged image from the internet) and cut out the face in the fondant. Add details with fondant tools. Use a paintbrush to add black cocoa powder for shading the pumpkin and darkening the eyes, nose and mouth of the jack.
Shading with the black cocoa powder definitely helps hide a lot of imperfections, so use it generously like I did. 😁 Add the fondant rope and fill the top of the cake with candy corn teeth and serve!