A way to clear score challenge while getting most of the rewards barring the final black trophy and prem coin is to use those elemental bane skills you can get by equipping the orbs or farming it in orb skill challenge. You only get one use out of it though per skill and requires you to revert a character to set up on top of it needing 6 SP use which you to have to either LB said character to 1 minimum or use the "skillful means" orb skill, which is also going to use a skill slot.
Note: the element bane skills CANNOT KILL SAID BOSS, you're gonna need to at least have the stats to damage them at minium.