Brimstone Cut is one of the dungeons added in the Definitive Edition. This dungeon contains the Split Shot Rifle upgrade, which you will need for:
The Split Focus achievement in ReCore worth 153 pointsKill 3 enemy corebots in less than 1 second with the Split ShotThe dungeon is straightforward, although the bosses can be tricky. It's one AP-3 and one FL1-R corebot that constantly change colours. Prioritize the AP-3 and take it out before it can be healed or covered by the FL1-R and you should be fine.