Factual error: Johnny shows Mavis the sunrise by keeping her back in the shadows. But if your whole body is in an object's shadow then you can't see the light source. The rising sun is reflected dead center in Mavis' eyes, which means the sunlight is touching her, which means she ought to be on fire.
Continuity mistake: When Dracula and his architect are going through blueprints of the hotel, Dracula is seen with a coffee in his hand. Mavis spits from the ceiling and it drops down to the table where the blueprints are. When they scan up to Mavis he has coffee, when they scan back to Dracula and his architect there is no coffee in his hand.
Plot hole: Frankie makes reference to fear of fire early in the movie in the scene with all the guests arriving at the hotel. And in the scene in the local village with the monster festival, a single match is uses to send him on a rampage. But throughout scenes in the hotel itself, there are lit candles, candelabras and torches throughout, most noticeably in Mavis' s room during the scene where her monster friends (Frankie included) are addressing her idea of going to a human village. None of this fire affects Frankie at all.
Continuity mistake: When everybody is playing bingo, the word bingo is placed correctly on the cards but none of the bingo numbers are in the right place. Plus, when the bingo lady calls out the numbers, everybody is stamping the number that was called under a different letter. Ex. When the bingo caller calls out N-27, Eunice stamps the number 27 but the number where she stamps it is under the letter I.
Continuity mistake: When Dracula is heading towards Mavis' room, one of the rooms he walks past is Room 174. When he finally reaches Mavis room, her room number is also 174.