In advance: Make coffin. Melt 10 oz. cocoa candy and pour into biscuit/brownie pan until 1/4 in. thick. Refrigerate until firm. Unmold on waxed paper-covered board; let come to room temperature. Using pattern and knife, cut coffin bottom and lid. Also cut 3/4 in. high pieces for sides, 2 each 1 5/8 in., 1 1/2 in. and 3 1/8 in. wide. To attach sides to bottom, start with a 1 5/8 in. top piece; run edge of piece along warming tray and position on coffin bottom. If a warming tray is not available, pipe a line of melted cocoa candy using a cut parchment bag and attach side piece. Repeat to attach two 1 1/2 in. sides, two 3 1/8 in. sides and remaining 1 5/8 in. side. Let set. To smooth gap between bottom and sides, run area along warming tray or use a hot knife.
Tint portions of melted white candy red, violet, black, gray and yellow using candy colors. Mold monster using painting method; refrigerate until firm. Pipe coffin handles using melted yellow candy. Position monsters and coffin lids.