The Grendel  is a legendary monster who battled the Geatish hero Beowulf.
Long, long ago, as part of a wager with a group of Vikings, the goddess Hel would send the ghost of the Grendel to test the bravery of their descendants. If the descendant failed, Hel would take their soul. After a 1000 years of this test being conducted, if more failed against the Grendel than won, Hel would claim all souls of the Vikings instead of helping them reach Valhalla.
In the present, Janine Melnitz was chosen to have her bravery tested by a Geatish ancestor. At midnight, the spirit of the Grendel would come for Janine. The New Ghostbusters with held all the scant details they knew from their liaison Jack Hardemeyer rather than let the test be turn into a glamorized public relations event and risk the safety of bystanders. Janine called Kylie Griffin for advice on the Grendel. Kylie wrote it off as a pushover and reiterated it was part of a test for bravery, a holdover from the Old World. 
At 6 pm, the Grendel manifested in the Duffy Square section of Times Square. When fired upon, the Grendel easily resisted Proton Streams fired by Special Agent Melanie Ortiz and Ron Alexander. It raised its arms and flipped the two. The Grendel then gave chase to Janine. In a panic, Janine called Kylie again. Kylie warned Janine not to run or she would make it stronger.  Janine fired a Boson Dart from her Compact Pack and dissipated the Grendel's left arm. While it was distracted, Janine wrangled and trapped the Grendel. However, the Draug appeared and informed Janine she failed because she solicited advice from another. The true nature of the test was for descendants to face the Grendel not knowing if it would kill them or not. To make matters worse, since Hel could no longer recall the Grendel, the wager would remain undecided. The Vikings were stuck as Draugar.
The Grendel is an atypical ghost with the unique ability to grow stronger the more its intended target tries to run away from it. It is also strong enough to easily counteract two Proton Streams.
- The Grendel manifested at 6 pm instead of midnight. While it was 6 pm in New York, it was midnight in the Central European Summer Time (CEST) timezone in Europe where the Grendel originated.
- His name and some likeness are based on the Beowulf poem about the Grendel.
- On page 4 and cover A of Volume 2 Issue #6, it was shown the New Ghostbusters' battle against the Grendel made the front page of a New York Today.
- In the Ghostbusters: Mass Hysteria hard cover collection, on page four, the Grendel appears in the lower left corner of the background.
- ↑ Draugar (2013). IDW Comics- "Ghostbusters Volume 2 Issue #3" (2013) (Comic p.3). Draugar says: "Grendel is coming."
- ↑ Kylie Griffin (2013). IDW Comics- "Ghostbusters Volume 2 Issue #3" (2013) (Comic p.9). Kylie says: "This is a basic test of bravery. Holdover from the Old World."
- ↑ Kylie Griffin (2013). IDW Comics- "Ghostbusters Volume 2 Issue #3" (2013) (Comic p.12). Kylie says: "It's not a typical ghost... if you run, it will just get stronger, and on one else can lay a hand on it."