MK JP got the Achievment for it but not the chest =\
For the last jump to be successful you have to jump after the clock is struck by lightning.
Better jump right when the lightning hits.
Don’t worry about the chest. 2 bad greenies worth 2s each and an exotic piece with bad stats that can’t be salvaged or sold.
IT’S A SWORD. THEY’RE NOT MEANT TO BE SAFE.