They share few similarities with Hoppers such as lacking heads. They have fatter bodies with a cut-opened slit.
BehaviorVis walk a bit slow around in the room aimlessly. When lined up with Isaac (horizontally or vertically), Vis will begin shaking violently and then fire a wide blood beam (similar to Brimstone) from their stomach for a few seconds. This blood beam may still damage Isaac for a fraction of a second after the beam has disappeared, so be careful.
- Some thought that the Vis' slits resembles to a vagina, but the game's creator Edmund McMillen deconfirm this, stating that Vises are just headless versions of the mini-boss Gluttony, as both behave in the same way and share the same body sprite; Both try to align themselves with Isaac in order to hit Isaac with their blood beam attacks. The only difference between the two is that Vis cannot perform the 8-way shot that Gluttony can. Thus, Super Gluttony also shares the same dual beam shot as well as the appearance of a Double Vis with a head.
- Edmund also confirms that the Vis is a reference to the Viseren Sisters, who were pair of bosses from his previous game Gish. They were born in The Womb and were separated. They can open the slices in their massive chests to give birth to small demonic enemies Nibblers. One is known as Vis Sister and the other is known as Sister Vis.
- Vis is Latin for "force/power", which may or may not be related to the enemy in the game. Viscera is a term involving the insides of living things. Since Vis uses blood beams that are fired from his chest, that could be a reason the enemy was named Vis.
- Vis resembles a Sheela na gig, a type of warding figure found in Ireland and Great Britain.
- In the original game, if the player has Wrath of the Lamb DLC installed, Vis may turn into Double Vis for a few frames when firing their blood beam.
- Only one side of the blood beam has a hitbox in Rebirth, dependent on which frame it was fired.