For higher difficulties (Veteran, Professional), prioritize defensive skills like Defense Lv. 3 and Breakout. Healing Item Efficiency also becomes more valuable. For offensive builds, combine Firearm Lv. 3 or Melee Power Lv. 3 with Critical Hit Lv. 3. Consider Infinite Ammo for specific weapons once unlocked, but only if you're not aiming for a high score. For Mercenaries, focus on skills that boost score, like J'avo Killer or Zombie Killer, alongside offensive and defensive skills. Adapt your build to the specific challenges of each difficulty and mode.
