This is an experience report about adopting agile principles on a huge, conservative, and inflexible environment of hi-performing mainframe applications. Working for critical bank and insurance projects, supporting airport infrastructures, security governmental processes, mainframes are the core backbone of many Fortune 500 companies. Such transformations bring unique challenges, and not only the technical ones. There are other challenges too, such as facing tons of legacy code and working with huge amounts of data. Both come with testing challenges as well.