There's no better way to spend Friday the 13th than by watching NBC's frightful two hour "Grimm" fall finale.

Starting at 9 p.m., NBC will premiere two back-to-back episodes of the fantasy drama series beginning with S3E7, "Cold Blooded," featuring a guest appearance by "Angel" star Alexis Denisof.

According to KSiteTV.com, an official synopsis states:

"As a deadly crime spree begins to surface, a century-old urban legend takes shape in Portland's sewers and becomes Nick's (David Giuntoli) latest case. In Europe, Adalind (Claire Coffee) meets Prince Viktor (guest star Alexis Denisof), who's come to bring those responsible for his cousin Eric's demise to justice. Meanwhile, Captain Renard (Sasha Roiz) responds to the recent attempt on his life. Bitsie Tulloch, Russell Hornsby, Silas Weir Mitchell, Reggie Lee, and Bree Turner also star."

Then at 10 p.m. EST, NBC will be the debut S3E8, "12 Days Of Krampus." The holiday-themed episode will feature an evil "Santa Claws" who comes to steal Christmas joy in Portland, notes DreadCentral.com.

The official synopsis reads:

"After a string of delinquent teens go missing, an old Wesen tale of an evil Santa who brings more than just a lump of coal may be the prime suspect. The investigation intensifies as Nick (David Giuntoli) and Hank (Russell Hornsby) take things a little too far. Meanwhile, Monroe (Silas Weir Mitchell) enlists Juliet (Bitsie Tulloch) to surprise Rosalee (Bree Turner) for their first Christmas together with unintended results. Elsewhere, Captain Renard's (Sasha Roiz) tour of Europe brings him closer to tracking down Adalind (Claire Coffee). Reggie Lee also stars."

The season finale starts Friday, Dec. 13 at 9 p.m. EST on NBC.

Watch a sneak peak below.