Argo is indeed a real story. The movie was based on a true operation that was carried out. Many of the details and characters are drawn from real-life counterparts.
There was no specific information about the Gundam's killing move against the Gundam. The search results mentioned some ultimate skills in the Gundam series, but it did not specify what the ultimate skill was. Therefore, based on the information provided, I am unable to answer this question.
Argo is indeed a true story. The movie is a dramatization of a real-life operation that took place. However, like many films based on true events, some details might have been changed or embellished for cinematic purposes.