>>92 already has links to download the episodes.

But if you really want to rip them yourself, you have a few options.

First of all, there are a lot of add-ons for Firefox for ripping videos from YouTube.
Personally, I use Video DownloadHelper. It has all sorts of settings, but you can use it without ever looking at the settings menu. Plus, if the video you want to download isn't an mp4, it also has a file conversion function, though I haven't actually tried it.
https://addons.mozilla.org/en-US/firefox/addon/video-downloadhelper/
And if that one doesn't work for you, there are at least 90 other extensions that match a search for "youtube download"

Second of all, I found this:
http://video.online-convert.com/convert-to-mp4
It allows you to put in a youtube link and it will convert it to mp4. It seems to work fine, though I only tested with one small video, so I'm not sure how good the quality would be for MLP episodes.

Third, you could combine the two. You could use a firefox extension to make sure you download the video at the highest quality available, and then use the site to convert it to mp4 if it isn't already (you can upload the video directly from your computer).

And of course, there are countless programs you can install on your computer for all sorts of downloading and video conversion.