It's a really annoying voice.
The ad ended with the creepy voice slowly saying, "Discount coupons available at Dunkin' Donuts."
The voice guy refused to break character for the Dunkin' Donuts tie-in despite the fact that it's basically impossible to instill fear when the word coupon is involved. Try saying "coupons" using your scariest voice. "Boo!" is decidedly scarier.
Note: 1,000 instant points of rad to those readers who actually tried saying coupons with a scary voice.