PixabayVideos is the best place to find free Halloween videos.
Just do a search ‘Halloween' then you can hover your mouse over each of them to see it moving.
There aren't many so it is quite difficult to find a specific video for free but the Pixabay license is CCO which means you can use them for anything. You don't have to give any attribution.
Search for ‘scary' and you will find a few more.
Another place is PexelsVideos but for ‘Halloween' there aren't many.
Videoblocks isn't free but is really good value at $99 for the first year then $149 after that.
You can download as much as you like of their membership content throughout the year with no limit on the downloads.
There's a lot more choice so a search on Halloween shows many results.
If you want music to go with these videos you can try FreePD. This is for free music and the ‘bizarre' category has some scary music.
The place that I use for music is Audioblocks which is $99 for the first year then $149 for the next year. I joined it and have downloaded a lot of music. You can download unlimited music and there's a lot if you search ‘Halloween'.
If you want to put all this together into great videos with music and text then what I use is Explaindio.
It is $59 for a year and I've got some videos on how to use it. They have a membership club that's $1 and worth joining as you can download a bunch of stuff.
Here are some videos about Explaindio: