In advance: Make cookie bases. Prepare and roll out dough. Use cutter to cut 20 rounds. Bake and cool. Tint 1 package Candy Melts gray using black candy color. Cover cookies; chill until firm.
Bake and cool brownie pops in silicone mold, supported by cookie sheet.
Cover with melted candy. Repeat 2 more times to totally hide brownie.
Using melted candy in cut parchment bag, attach pops to center of cookies. Pipe tip 3 bead borders. Attach confetti sprinkles around cookie edge. Cut bottom half off spice drops; attach rounded top to pop. Let set. Pipe aliens with buttercream. Use tip 9 to pipe 1 1/4 in. round head (smooth with finger dipped in cornstarch). Pull out tip 6 arms, tip 3 hand and fingers, tip 2 hair. Pipe tip 3 dot eyes, tip 1 dot pupils and zigzag mouth, tip 2 dot cheeks. Position on stand at party.
*Combine Violet with Rose for violet shown. Combine Leaf Green with Lemon Yellow for green shown.