no IDK how that works, but it's nothing special, it's just Dracula comingt out of the closet and getting rejected by being killed lol
they had a slot called Castlevania the Metal, it maybe if you have play Castlevania the Arcade along with the Metal to unlock it. I truly don't know but the game even talks about it. and you can get metals that let you use your score instead of hearts. that you can unlock in the setup file same as the secret charter the little witch. so perry sure it's unlocked with the slot game. so sadly we probably can't unlock it, unless it's in the setup file too. IDR but you can watch it by looking in the folders of the files of the game. they aren't no real protection stopping you from watching it, or editing it, it's just movie and wav files. that's how I was able to put Alucard into the opening story in game.
Edit
I ran across a reply talking about the joke ending. here it is
Arapose — 05/30/2023 8:02 AM
Now I wonder how can the player spot the duck in order to get the joke ending, and also how to spot the UFO in Silent Hill Arcade?
bojo5150 — 05/30/2023 8:39 AM
You have to beat the game and play a 2nd time
so from what these two said you have to beat the game and play again on a second playthrough. and then you will see a duck somewhere, and have to shoot it with a sub weapon, if you get the duck you get the homo Drac ending.