Each special weapon has a different purpose. Weapon properties include single-shot damage, ammo capacity, rate of fire, and damage per second (assuming continuous fire). Try each and see which situation suits a weapon or combination of equipped weapons.
Spread Gun: Fires three medium sized bullets straight ahead, to the left and to the right. Higher levels of this weapon will fire more bullets at a time and allow you to carry more ammunition.
Vulcan: A rapid-fire cannon. Fire stream widens as level increases.
Surge Shot: Fires bullets that can pass through walls. High damage, fair rate of fire. Higher levels will increase each shot's size.
Plasma Sphere: Fires a large, slow-moving projectile that goes through walls and enemies alike, doing continuous damage to any enemy in its path. Higher levels will increase its size and rate of damage.
Rockets: Explodes on contact. Higher levels increase damage and blast radius.
Missiles: Explodes on contact, homes in on the nearest enemy. Does less damage than the rockets. Higher levels increase damage and rate of fire.
Grenade: Moves quickly, does not explode on contact, but after going a specific distance. It has a wide blast radius. Higher levels increase damage and blast radius.
Specialized Tracking Explosive (Spectre): Laid wherever Seraphine uses it. When an enemy gets close, the Spectre will attach to that enemy. Pressing the assigned special weapon key while a specter is active will detonate it. Higher levels increase damage and blast radius.
Drone: This weapon will follow you and fire along with your repeater. Its "ammo" serves as its health while it's in use. The drone repairs itself over time. Higher levels will improve its firepower and durability.
Force Field: This weapon will provide an external shield that does a fraction of the damage enemies can deal back to them on collision. The shield loses durability over time, but it absorbs enemy collisions and projectiles alike, before they can reach Seraphine. Higher levels will grant it much higher capacity and (at level 3) allow it to regenerate Seraphine's own shield strength.
Caissie-Jonze Bullet Attenuation Tool (CJ-BAT): This melee weapon will deflect red projectiles fired toward the nearest enemy, and do contact damage to enemies. Reflected projectiles are green. Higher levels increase damage of each swing and the maximum damage value for reflectable projectiles.
Knights Templar Lance: This rail cannon allows you to charge a shot up to three levels. That shot will quickly zip through all enemies in its path. It has the highest single-shot damage in the game.
Death Claw: An experimental beam saber, its short range is offset by its ability to do great damage to anyone hit by it over a short period of time. It has the highest damage per second and rate of fire in the game.
Ultraviolet (UV) Flash: This weapon will instantly kill all enemies on screen that aren't immune. No points are gained by enemies killed in this way. It does not have very much ammo.
These optimal weapons will not be available through most of the game, and will require the completion of special optional stages in order to acquire them.
Crisis triggers provide a way of giving Seraphine a fighting chance when she is one hit away from defeat. They activate automatically, with some requiring a gauge to be filled. Picking up items restores the crisis gauge based on the shield strength each item recovers. Picking up equipment fully charges the gauge.
Awareness: Time will appear to slow down for ten seconds when this crisis trigger is activated. Seraphine is unaffected. Crisis gauge length: 10
Mercy: Grants five seconds of invulnerability when activated. Crisis gauge length: 15
Patience: After fifteen seconds at zero shields, your shield gauge will fill up to 1/4 of its maximum.
Endurance: The next item you pick up while at zero shields will restore twice the usual shield strength.
Impatience: Any items on screen will be automatically acquired. Crisis gauge length: 25
Transience: Your vulnerable area shrinks from 8x8 pixels to 1x1, and a tiny red dot will appear on Seraphine, representing that area.
Disruption: A great flash will cover the screen for a split second, doing massive damage to everything on screen. Crisis gauge length: 20
Belligerence: Your speed and damage will triple, but after ten seconds the game will be over until you recover some shield strength.
Redemption: When you would otherwise be defeated, you instead fully recover your shield strength. Crisis gauge length: 50
Hypochondria: This adds a second damage "stopping point" at 200 shield strength.
Courage: This quadruples the points gained by acquiring items and defeating enemies.
Fury: This doubles the damage Seraphine deals.
Dodge Tools add a secondary function to each dodge, triggering whenever Seraphine performs one.
Tumble: This adds extra movement to Seraphine's dodge, but she is vulnerable during the extra movement.
Stability: This prevents movement while dodging, but preserves the invulnerability of the dodge.
Apparition: This will generate a stationary energy trap that does damage over time to any enemy in its range. 5 second cooldown.
Rock and Roll: This turns the dodge into a melee attack of sorts. 5 second cooldown.
Finesse: If Seraphine dodges through an enemy or a projectile, time appears to slow down for one second.
Blink: This gives the dodge a longer startup, but greatly increases its speed and shortens its recovery time.
Dot Eater: Dodging is no longer invulnerable, but moving through enemies and projectiles adds to your score and to the crisis gauge.
Health (small): Restores 500 shield strength.
Health (large): Completely restores shield strength.
Ammo (small): Restocks the ammunition of each special weapon by 1/5 of its capacity, restores 100 shield strength.
Ammo (large): Fully restocks all special weapons, restores 200 shield strength.