(at around 11 mins) At the beginning of the movie, the car the characters take to the party has Romanian plates. Later on, the plates are American.
(at around 1h 3 mins) When Chelsea returns to the house she runs through the front door and the door behind her is still open. In the next shot, the door is closed.
(at around 1h 27 mins) When the Host is toying with the Lament Configuration at the end of the movie, the length of the cigarette varies in every shot.
(at around 1h 28 mins) After the Host is taken to hell, Chelsea and Jake are shown driving down the road. At first there is no license plate visible on the rear door of her SUV. A few shots later the license plate appears.
(at around 17 mins) When Mike and the others are in the Hellworld party host's study, he's wearing a gray hooded sweatshirt with no jacket. When they go down the stairs into the lower parts of the house, he's suddenly wearing a leather jacket over the sweatshirt.
When Allison calls Derrick to see if the phones work, he answers. When it cuts to Allison, then back to Derrick, it shows the call is still ringing and has not been answered. Also Allisons name wouldn't show up on the caller ID as they each took a random phone. Theres no way the Host knew beforehand who would get which phone.
At 44 minutes when Derrick's head lands in the bowl it is already full of blood and causes a splash of blood.
When The Host is sliced up with two slashes of a chained scythe by a cenobite at the end of the film, the first slash severs his arms. They however, do not fall immediately because of gravity which is what should have happened, but slowly fall off after the second slash.