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By default, after beating one of the eight main bosses, you'll be given the options "Weapon + Life" and "Weapon + Energy". Pick one to get either a Life Up or an Energy Up. However, if the boss was on level 8 or higher, you instead get "Weapon + Life +" and "Weapon + Energy +" options. Then you get an additional Part along with the Life Up or Energy Up. The Part you get depends on which option you pick; this means you can't get all 16 Parts in one playthrough. The most Parts you can get is 8, and for that you'll have to waste time at the beginning. The bosses' levels rise as the countdown progresses, so you'll have to enter stages and deliberately lose all your lives, not fighting any bosses until the first boss's level reaches 8. That means you'll have to cut it close to stop the collision. Also, once you've earned a Part, you still won't actually get it until two stages later.

Part Name	Option	Boss	Effect
Life Up	Weapon + Life	All	This increases of your character's life meter, just like a Heart Tank.
Energy Up	Weapon + Energy	All	This increases the maximum size of your character's weapon energy meter.
Shock Buffer	Weapon + Life +	Grizzly Slash	This decreases the amount of damage taken by half, and keeps you from being knocked back after taking a hit.
Hyper Dash	Weapon + Energy +	Grizzly Slash	This makes your character dash faster.
Super Recover	Weapon + Life +	Duff McWhalen	This makes life and weapon refill capsules restore twice as much energy as normal.
W-Energy Saver	Weapon + Energy +	Duff McWhalen	This makes your special weapons use half as much energy.
Quick Charge	Weapon + Life +	Squid Adler	(X only) This makes the X-Buster charge twice as fast.
Z-Saber Extend	Weapon + Energy +	Squid Adler	(Zero only) This makes the Z-Saber project a small crescent wave in front of it to increase its range.
Burst Shots	Weapon + Life +	Izzy Glow	(X only) This allows you to have 5 buster shots on-screen at once instead of 3.
Shot Eraser	Weapon + Energy +	Izzy Glow	(Zero only) This enables the Z-Saber to block most enemy shots.
Anti-Virus Guard	Weapon + Life +	Dark Dizzy	This makes you twice as resistant to Sigma Virus infection.
Virus Buster	Weapon + Energy +	Dark Dizzy	This enables your standard weapons to destroy Sigma Virus drones.
Jumper	Weapon + Life +	The Skiver	This makes your character jump higher and further.
Speedster	Weapon + Energy +	The Skiver	This makes your character run faster and jump further.
Speed Shot	Weapon + Life +	Mattrex	This makes the X-Buster or Z-Buster's shots go faster.
Buster Plus	Weapon + Energy +	Mattrex	This makes the X-Buster or Z-Buster do more damage.
Ultimate Buster	Weapon + Life +	Axle The Red	(X only) This makes every shot you fire fully charged, including special weapons (if you're using an armor that allows charging special weapons).
Z-Saber Plus	Weapon + Energy +	Axle The Red	(Zero only) This makes the Z-Saber do more damage.