Crunchyroll is listing the special episode of 86 as episode 12, but whatever you call it, the episode – titled “Coquelicots Blooming Across the Battlefield” – is just a standard recap episode. It is narrated by Lena and shown entirely from her viewpoint, with the only new shot being the one above, which is shown in the episode’s last few seconds as a preview for the second cour. (The ‘mech above is called a Reginlief, but saying anything more than that about it would constitute spoilers, so I won’t comment further.)
Frankly, other than the preview image teaser, this episode would have been better-served airing right before the series returns in October. If you have not already checked it out, that is when I recommend watching it.