This might be tricky at first, or maybe the first few times, but once you get the hang of it, it's pretty quick.
For those vidoes you can't get the video IDs from, but have the episode IDs, try this:
In the URLs you posted mention the episode IDs(1721976, 1721977)
Append one of those IDs to the end of this URL:
Now for the "wolf watch" show (1721977), it works as intended.
It brings up a playlist of the episode, of all 4 clips.
The video ID for each clip is listed at the bottom of the page:
You would append these video IDs to the end of this URL:
(When you get your links from the XML pages, copy starting from /gps.alias/ to append to the final URL to watch/download)
MTV cuts their episodes into clips though, so in this case 4. So if you want to download this show you will have to download all 4 clips and join them together using some sort of mp4 joiner program to create a single seamless video.
Now for the actual episode (1721976), all I'm getting is a white page when I append the ID to the end of the URL above.
If I open up the browser console, I can see that the page is coming back "ACCESS DENIED". So they are intentionally blocking access to the playlist.
This would have been the easiest way since it would list all the video clips included in that episode, along with their video IDs, but there's another way if you are determined.
In Firefox press "CTRL + SHIFT + J"
This will open up the browser console log.
Now reload the video for the episode you want to rip.
In this case, teen wolf season 3 episode 18.
Now when the video begins to play ("previously on teen wolf..")
Open up the browser console log and look for a bunch of text that looks like this:
v11=Show Clip - Full Episode : Previously On_1002038
v12=Teen Wolf : Full Episodes
c21=Show Clip - Full Episode : Previously On_1002038
c22=Teen Wolf : Full Episodes
v28=Show Clip - Full Episode
Right away we see the video ID for the beginning of the episode. It's 1002038.
Since the episode is always cut into multiple clips and the video IDs are almost always numbered consecutively, we can reasonably guess that the very next clip in the episode will be 1002039.
So we test it out by checking it with this URL again:
Sure enough, it loads the XML page with the available bitrates/resolutions.
Next you would check 1002040, 1002041, etc, etc. until you have the full episode.
The numbers are not always consecutive, so if you run into a "page not available" video ID, try the next one.
For example 1002040 is a legitimate video ID, 1002041 is not. 1002042 is. So it skips over 1002041 for some reason.