The Evil Force is a large, disembodied demon-like head with an aura glowing out of it. Its main attack consists in lunging in to Shanoa, trying to touch her and deal some damage. If its prey is within range, it will open its mouth and quickly stick out its tongue to attack with it. Evil Forces are found prominently in Mystery Manor and in Dracula's Castle, although they can appear in Minera Prison Island if a spotlight shines over Shanoa (this does not apply to the room near the end of the level, as the enemy is replaced by a Tin Man instead).
It also resembles Gofer from the Gradius series, as Gofer was a demonic humanoid head created by the Dark Force (Bacterian). It is not uncommon for Konami to pay homage to their other games.
The Evil Force may also be a reference to the main antagonist of the Evil Dead series, which is sometimes referred to as the "evil force". In addition, it somewhat resembles the physical manifestation of the force as seen at the end of Evil Dead II.