Midsummer Nightmares
(2011)

Danielle Waters (Stacy Freeders) is the killer. She kidnapped Audrey Small (Julie Sherwood) from her costume party, killing several of Audrey's friends, including her boyfriend and her best friend/roommate Liz (Kelci C. Magel). Danielle targeted the group over jealously and anger since they threw away numerous opportunities to better their lives while Danielle was stuck in their small town with her fundamentalist family. Danielle was particularly jealous of Audrey getting a full college scholarship after performing in a high school play only to turn it down, something the envious Danielle wanted for herself.

Unbeknownst to Danielle, Audrey's neighbor Rob (Scott Gillespie) had seen her get kidnapped and followed them. Rob unties Audrey from her restraints as Danielle returns to kill Audrey. Audrey and Rob fight Danielle, with Audrey eventually getting the upper hand and bashing Danielle's skull with a trophy. The film ends with Rob and Audrey about to call the cops.

After the credits, there is a post credit sequence. We see a close up of Danielle's face. Her head turns and she gasps for air. It appears she wasn't dead after all...

Thanks Tim (Spectre)!