Well that settles it, I'm getting this DLC day-one. In a Miiverse post, Eiji Aonuma announced that Link's trusty steed Epona will be included in the October 16th Master Quest DLC drop for Hyrule Warriors. The interesting part is that Epona won't be an individual character; instead she will function as an alternate weapon for Link. This makes sense I suppose as it would be kind of funny to just have a horse galloping aimlessly around a field full of enemies. Link and Epona were always most effective when teamed up.
Considering the awesome mounted combat in Twilight Princess, I can't wait to see how crazy it will be in Hyrule Warriors. There isn't any more info on what else the Master Quest DLC pack will include, but it was cool of Aonuma to give us a sneak peek.
Source: Nintendolife