Almost unique to the Gradius franchise, the Sub Bosses in Gradius games usually consist of specialized groups of enemies, and you must either survive for a set period of time or destroy them all.

They are sometimes referred to as Panic Sections or Skirmishes.

Occasionally actual Core Ships and special enemies will appear mid-level - but this is rare for the Gradius series, and occurs more often in the Parodius series. The Parodius games and Gradius ReBirth are the only games to use separate music for Sub Boss battles. In most cases these sub boss battles occur directly before the stage boss.

This tradition started in the original game and has stayed ever since. Whilst many Sub Bosses in the first game have gone on to become traditions in the overall Gradius franchise, other games have introduced their own specialized enemy skirmishes.

Notable Sub Bosses:

• Volcano : Present in many games in the series, the volcano is a popular element.
  
• Zub Rush : Appearing in the majority of Gradius and Parodius games, the Zub Rush has become a staple in the Boss Rush levels, allowing the player to gain additional power up capsules.
  
• Iron Maiden : Recurring sub-boss that later showed up in Parodius Da! in a extremely difficult section of the game.
  
• Zigzag : A one shot Sub Boss in the Game Boy version Nemesis, that got expanded upon to form a fully fledged boss fight in Gradius ReBirth, the Moai Orb.
  
• Jumping Moai : `A sub-boss that showed up in nearly every port of Salamander, and got a significant health boost in the Commodore 64 version.
  Stronger, singular versions of this boss show up in later games as well.
  
• Fortress Valis : Starting off as a regular Boss in the first Salamander, this Gunwall got knocked back into being a Sub Boss in several ports.

Minibosses / Panic segments
Traditional / Recurring	Volcano • Zub Rush • Iron Maiden • Re-Bone • Fortress Valis • Jumping Moai • Dogas
One Shot	Mother and Child • Tentacle • Tornado • Tyran Pace • Zigzag • Amb • Sodd • Sinar • Crash Bam