Imagine you're Future Trunks and you live in a world where Android creations by Dr. Gero have taken over the world, destroying entire cities and wiping out much of the planet's population. Though you travel back in time to save Goku from a fatal heart condition in an effort to prevent that apocalyptic future from ever occurring, you return to the future only to see that nothing has changed and you've merely created an alternate reality.
Yet the trip was not without its benefits as Trunks was able to train and learn techniques from Goku, Vegeta and the other Z-fighters which raised his power levels to such heights that he was easily able to defeat the Androids and Imperfect Cell of his timeline. With that complete, you'd think Trunks and the remaining survivors would be able to rebuild civilization. However, years later, a new threat emerges in the form of an evil Goku and a corrupt Kai who have used the Super Dragon Balls in such a way that even the God-Ki empowered Vegeta and Goku are struggling to find a way to defeat them. It seems this current situation was simply too much for Future Trunks to deal with as his explosion of grief and anger has led to yet another new Super Saiyan transformation (which is currently untitled) seen in the closing minutes of Dragon Ball Super episode 62. Just how powerful this new transformation makes Future Trunks remains to be seen but you can bet we'll find out tomorrow when episode 63 hits Japanese airwaves.
YouTube Dragon Ball expert Geekdom101 breaks down the transformation and speculates on what's to come in the video below.