Game Mechanics

Plasma Cypher

The Plasma Cypher is Strider Hiryu's primary weapon, and can attack in all 8 directions. It is also a button masher's best friend: you can attack as fast as you can mash the button. Attacking while moving does not slow you down. Charged Cypher Strikes double damage and range for a single hit. The charge time is very short, but it is significantly less DPS to try and chain Charged Strikes instead of mashing uncharged ones. The attack is still useful as a first hit on enemies and for breaking many shields. It also enables you to use Charge Boosts, explained in Movement Techniques. Of the 4 Plasma Types that you gain access to, Explosive Plasma deals extra damage and is the one you will use most often in a speed run. Ice Plasma turns enemies into platforms and disables them completely, which may have speed running uses.

Kunai

Kunai can be thrown at any analog angle independent of your movement by using the right analog stick. This allows you to dispatch distracting or troublesome enemies without slowing down to go attack them head-on. The optional Kunai upgrades dramatically increase their effectiveness if you take extra time to grab them. If killing them is the priority, Magnetic Kunai work best at long ranges, while Explosive Kunai work better at close ranges. If disabling them is the priority, Ice Kunai work amazingly but some strong enemies are immune.

Charge Strike Meter

That is the official name of the HUD item in-game.  Found under "How To Play" in the options menu.

Shortened as Charge Meter, often referred to by other names such as Rage Meter, the Charge Meter is the most important aspect to quick boss fights. The Charge Meter is filled by dealing damage: details below. When filled, Hiryu enters "Charge Mode" for 5 seconds, in which all attacks are 2X damage and 2x range i.e. they all become Charged Strikes, hence the name. The game slows down on activation, giving Hiryu brief Matrix style bullet time for easy damage dealing.

You lose Charge when you take damage, but the amount is variable with different attacks based on the damage taken. Example: walking into an acid glob from an Insect enemy loses about 10% charge, but getting punched by a Heavy Mech loses more like 25%. Avoiding damage in boss fights is thus more key in this game, not only for the usual reasons like hit stun wasting time, but because it delays your Charge Mode. You will lose all Charge after 5 seconds of not dealing damage.

EVERY individual hit always builds 2.5% of Max Charge, no exceptions. This value is multiplied by the number of enemies hit at once when applicable. This value assumes Charge Mode activates at 100%.

Cypher Strike:

Standard Cypher Strikes are the best way to build Charge; each hit grants 2.5% which means 40 hits to fill the bar. You may need to hone your button mashing skills to effectively run this game. Hitting multiple enemies at once with this (or any) attack multiplies the Charge gain.

Charged Cypher Strike:

Although they do double damage, Charged Strikes still build the same amount of Charge Meter. The equipped Plasma type makes no difference in Charge gain.

Slide Assault:

Too slow at racking up hits means poor Charge gain, use only for movement and passing through enemies.

Kunai Throw:

The default Kunai throws 3 projectiles, but optional upgrades can increase this to a total of 7 projectiles. Charge built by multiple projectiles stacks, and shotgunning Kunai is HIGHLY effective and recommended. Unfortunately, in a speed run it is unlikely you will have time to grab tons of Kunai upgrades to actually abuse this fact. Furthermore, each projectile can only hit 1 enemy. The exception is the optional Explosive Kunai upgrade: Each explosion builds the usual Charge but has a small radius that can affect more than one enemy. This upgrade delays the damage, and Charge, until the explosion occurs.

Plasma Catapult

Builds the same amount as a Cypher Strike.

Option A "Dipodal Saucer"

The Saucers themselves deal collision damage and build Charge on contact. Cypher Strikes cause the Saucers to fire projectiles, which also build the same amount of charge additively with Saucer collision damage AND Cypher Strikes themselves. This results in a frenzy of damage at close ranges, and very efficient Charge gain. This is the optimal way to fight all bosses when in melee range.

Option B "Tetrapodal Robo-Panther"

The damage increases with each successive hit, but Charge gain is static. Can hit the same enemy multiple times based on terrain.

Option C "Robot Eagle"

This attack often seems like it builds more Charge than normal. It actually hits single enemies twice extremely quickly, and builds additional Charge. This is based on the enemy's life; If it could only survive 1 hit, only 1 hit's worth of Charge is gained.

Glitches

Out of Bounds (OoB)

Discovered by EliteAssass1n
This glitch can be performed in any Save Room. To perform, simply climb onto the ceiling at the corner where the highest flat part meets the angle going down. Once in position, wiggle the shit out of top 180 degrees of the analog stick. Alternatively, try to mash Left, Right, and Up all at the same time. Once successful, Hiryu will have climbed up into the ceiling and be able to freely move outside the normal boundaries. Methods and locations to re-enter the map vary. Videos of the glitch can be found in Additional Resources.

Kunai Through Walls/Doors

Discovered by ...
Kunai can pass through some surfaces to hit the switches for Kunai doors from the wrong side. Many of these doors were intended to be one-way, but can be opened from the wrong side with this glitch. Most optional Plasma Kunai upgrades make this glitch harder to perform, but the Magnetic Plasma Kunai upgrade makes it much easier as Kunai now readily penetrate all surfaces.