Tommy Robbins races past the skeleton pirate, pig butcher and gothic vampire costumes without even a glance. He’s on a mission. Tommy is 7, so Halloween is everything. And the sweet little Medford boy with brown hair came to Spirit Halloween in Marlton with a plan. “I either want to be the grim reaper or a killer clown,” Tommy announces with a charming, half-baby teeth smile. He suddenly stops in his tracks, his brown eyes wowed by a wall display. There isn’t just one murderous clown costume here. There’s Chaos Clown. Krazy Clown. Wacky Mole Clown. And, if you’re into medieval homicide, Sinist…