Here's a demonstration of Dracula being taken down in only 2 of his attack patterns. You need a little luck so that Dracula will appear in a position near the middle so you can shoot him faster, and he needs to use a non-threatening attack (apple spam is probably the best). In addition to luck, you'll need to be able to mash rather quickly.
It's possible to take him down in one phase if you satisfy a few conditions: -Dracula must spawn near the middle to reduce the distance your bullets have to travel -Dracula must use the apple spam attack -You have to mash like you've never mashed before
BTW I disabled effects, so that's why Dracula's cape looks a little different when he starts his apple spam attack.