Dark Marker

 is a gun. The gun can be charged to fire a red projectile and a blue projectile at the cost of 10 ammo, both of which curve and meet at one point. If the two projectiles meet, they will create a large explosion and trigger a blank effect.

Trivia

 * The mechanic of the charged shot is a reference to matter-antimatter annihilation, whereby 100% of the mass of the matter and antimatter are converted into energy. (It has a synergy with Antibody because of this)
 * Instead of strong and weak particles, in reality the strong force and weak force are two of the four fundamental forces, alongside gravity and electromagnetic force.
 * The synergy might also be a reference to the game Antichamber.
 * The phrase "Big Bang" and the way Dark Marker's bullets react might be a reference to the Big Bang, the explosion that occurred in space.