I’d like to go over one of the most bugged on question of all regarding the single player campaign of the game – Why do you get, after finishing the campaign, that you have only completed 25 of the 26 missions available in story mode ?
The answer is rather simple as the mission missing is actually a secret mission. I will try to reveal as little from the plot as possible but be warned that the following part might contain some spoilers, so in case you don’t want to know what this is about, read no further.
While playing the single player campaign, once you finished roughly 75% of the game you will have a mission called Media Blitz. In this mission you will have access to the almost hero unit, the one called Odin (it really is just a pumped up Thor from the multiplayer), controlled by Tychus. While this mission is active and before you do complete the campaign or before you go to Char, while in the mission you need to follow a path from your base, close to the Dominion base on the bottom right, and turn right just before reaching the first communication tower.
You will then find a weird looking building with the name of “Korhal Citizens”. By the way, you don’t need to use Odin to destroy this, any unit can destroy it, but be careful because you will need to use the attack command on it, as simply right clicking it won’t do the job. By destroying it you will see that once the rubble clears a special glowing item will appear named “Secret Documents”. By picking this up you will unlock a special hero type mission which is very similar to the ones you would have in Warcraft III.
The secret mission is massive amounts of fun and will give you the 26 out of 26 when ending the campaign. As a small info this will give you the Jim Raynor icon, actually just completing the single player will do that, but in order to receive 3 more icons for your Battle.net 2.0 profile you will have to complete 29 missions. This is actually achieved by playing both parts in the “choice” missions. For example when you have to chose between Nova and Tosh and so on.
Either way, you now know how to get that one done as well. Until then, enjoy the campaign and remember that by finishing it in one go on Brutal you will unlock Hard and Very Hard icons as well.