The third film

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I was wondering if they were going to do a third film myself, and I actually have a plot in mind.

Noticing that Johnny is showing signs of aging, Drac starts thinking about the heartbreak he went through when he lost his wife. Not wanting Mavis and Dennis to go through that same pain, he suggests turning him, but Mavis insists that she loves Johnny as he is. Drac decides to take matters into his own hands, maybe even trying to make turning him look like an accident. Enlisting his friends' help, he tries to turn Johnny without being discovered, or maybe even setting up life threatening situations that Johnny gets caught up so the only option left is to turn him or else he'd die. But these plans keep backfiring on him in some way, much like how he tried to bring put Dennis' vampirism. The real problems start when a vampire hunter, perhaps a descendent of Van Helsing, arrives to check out the hotel, so Drac has to also try and trick the hunter into thinking it's a human hotel by having everyone pretend their human. This makes his attempts to change Johnny even more difficult.
Of course, at some point Mavis finds out that Drac is secretly trying to turn Johnny, causing a big argument. This argument is overheard by the vampire hunter, who realizes that this IS a monster hotel after all, and he tries to kill Drac, Mavis, and Dennis. Just before he shoots Mavis, Johnny steps in to defend her, taking the hit, but they both go down. And as the vampire hunter moves in for the kill on either Drac or Dennis, Johnny comes back, revealing that Mavis bit him to save his life, and defeats the vampire hunter.
After it's all over, Johnny reveals that he's completely cool with being a vampire, and so is his family when they find out.