The Spectre is a variation of the Pinky. It is identical in most regards, with the main difference being its near-invisibility.
The Spectre is normally only visible as a faint translucent outline of a Pinky demon, but the creature itself is unchanged.
Spectres have identical AI and attacks to Pinkies, performing straight-line charges at long range that will stun them if they collide with an object, and vicious bites at close range.
The only major changes are related to how the player fights them: Spectres, due to their cloaking capabilities, cannot be targeted by weapons that lock on to their targets. This means that the Heavy Cannon's Micro-Missiles and the Rocket Launcher's Lock-on Burst will not target a Spectre, the Plasma Gun's Microwave Beam cannot lock on to them, and the Meat Hook will not treat one as a target. This can be nullified by hitting a Spectre with a Freeze Bomb.