For further mission-specific tips or deep dives into the nightmare difficulty, you can check community resources like the Steam Community Guides or Tactical Hints for Nightmare .
To succeed, you must assign each troop a specific task based on their strengths: alien-shooter-td-darksiders
These are essential for late-game survival. Place them at the very start of the enemy path to strip armor before they reach your other units. Focus upgrades on "damage to armor" first. For further mission-specific tips or deep dives into
Cryo units slow down fast enemies, allowing your high-damage troops more time to fire. Place them at corners for maximum area impact. alien-shooter-td-darksiders
Each class has unique characteristics. Send your troops for training between missions to develop specific combat skills.