The Benefactor is indeed a banshee - a banshee that our gang of teen heroes once trusted.
The recently aired season 4, episode 9 of "Teen Wolf" titled "Perishable" opens with Parrish (Ryan Kelley) locked in a car while Haigh douses him with gasoline and lights him on fire.
Meanwhile, Lydia (Holland Roden) and Stiles (Dylan O'Brien) consult Sheriff Stilinski (Linden Ashby) to check whether Lydia's grandmother, Lorraine, is dead like everyone thought she was. And just as the Sheriff wonders where Parrish is, the hottie deputy shows up at the precinct alive, and attacks Haigh.
In an attempt to know what supernatural being Parrish is, Lydia takes him to Scott (Tyler Posey) and Derek (Tyler Hoechlin). Derek, however, has no clue what Parish could be.
Lydia then starts to dish Lorraine's backstory. Lorraine, loved another woman named Maddie. One day, Lydia's granny got the feeling it was raining even though it wasn't. She called Maddie, who was planning a boat trip, to tell her to be careful. But Maddie went out on the boat anyway, and died in a storm. Her death caused Lorraine to seek the help of psychics, including Meredith Walker.
Lydia and Stiles are able to figure out the code to decipher the last part of the dead pool, which shows the names of the patients at Eichen House who all had committed suicide, including Lorraine. The duo then goes to Eichen House and bribes Brunski so they will have access to Lorraine's files.
The two get suspicious when they see Brunski has a mix tape similar to the ones handed out by the Benefactor. Soon after the pair finds themselves tied up with Brunski claiming he was only helping all the people he killed. He forces Lydia to listen to a tape of him killing her grandmother. On it, Lorraine tells Brunski not to hurt her granddaughter.
Brunski then decides to kill the two. Good thing, Parrish noticed that Brunski's name was on every suicide report, so he has come to the rescue, and shoots Brunski.
As the trio celebrates the death of the Benefactor, Brunski laughs. "Sorry, bros, I'm not the Benefactor!"
Then Meredith, whom viewers thought committed suicide, skulks around the corner and reveals she's the benefactor. "He wasn't on MY list... but he was a bad man," she said of Brunski.
The big reveal was criticized by some viewers, including Starpulse's Emily Steck. "I can't help but feel cheated... of this great big reveal," she wrote. "There were convoluted plots that were poorly explained, awful pacing and awkward edits. This episode is the worst episode of recent memory for 'Teen Wolf.'"
The unfolding of Lorraine's backstory is also slammed by many, including BuddyTV's Morgan Glennon, describing it as a "hastily dumped exposition." "[It's] like what would happen if you took the plot to a Nicholas Sparks movie and turned it into a show on ABC Family," she wrote.
But now that the identity of the Benefactor was already revealed, "Teen Wolf" must be able to provide a logical explanation as to how Meredith has become the dead pool's author, Entertainment Weekly reported.
