If the shoot key is pressed, the player slashes in front of them and sends out a wave at the end. The wave can bounce off of surfaces and soon goes upward in a parabola. However, the projectile will not fire if any hits from the melee land. You can tell if damage taken was from the projectile via a blue slashing effect appearing on the damaged enemy.
If the slide key is pressed with the weapon equipped, the player dashes and slashes in front of them, damaging anything in the player's path. The player is invincible during this dash, but is immediately vulnerable afterwards. This, coupled with the dash's underwhelming damage, means it's best utilized for plowing through enemies with low health (unfortunately it can't destroy Spines) or bypassing damaging hazards with small hitboxes.