At the end of the Terminals, you'll face The Slavers, a group of three larger, more durable enemies. Each Slaver has a different attack pattern: one uses a melee weapon, one a ranged weapon, and one a shield. Focus on one Slaver at a time to reduce the incoming damage. The ranged Slaver is often a good first target.
Utilize your dodge roll to avoid their attacks and create openings. Secret Skills like Bellow or Squirt Lure can be very effective here for crowd control or distracting enemies. Keep moving, use your health tonics when needed, and don't get surrounded. After defeating The Slavers, you'll find another Core. Return to the Bastion to restore another structure, perhaps the Memorial, which offers challenges.