Legendary SSJ5 is a new Super Saiyan transformation that only Broly has obtained. This form is very similar to the LSSJ form. Broly obtained it after getting defeated by Goten and Gohan, after the massive Kamehameha that Goten and Gohan made Broly was in a near death situation thus getting a HUGE zenkai boost. After getting that boost, he went off to a distant galaxy and started intense training so that he can finally surpass Goku. LSSJ5 multiplies the user's power by 8,000x their power from the previous form. In the LSSJ5 form your power increases as time passes, much like the original form. (LSSJ). But it goes slower because you are already so strong.