In the short film Puppy! (2017) Released a year before this feature film, Mavis can be seen reading the travel brochure for the actual cruise ship from Hotel Transylvania 3, months before it was officially revealed to the public.
The VFX team had to build all the individual ships that were in the Bermuda Triangle because they wanted a believable structure when being stacked.
The Chupacabra is a Mexican folk legend (goatsucker) monster who is known to drink the blood of goats. This is why the bartender gives him a goat in a glass when he asks for a drink.
Genndy Tartakovsky didn't want the fishmen to bend forward because fish can only bend sideways so he asked animators to have the least amount of movement for them as possible; sometimes in scenes only their mouths or eyes move.
The scene where Johnny sees a gremlin on the wing of the airplane is a tribute to Nightmare at 20,000 Feet (1963).