When used for the first time, Isaac creates a blue portal under where he is standing. The next time he uses the item, he creates an orange portal under his feet. Isaac can then walk over either of the portals to teleport instantly to the location of the other one.
Activating the item more than twice will replace the older of the two portals.
Upon teleportation, Isaac is granted with a short invulnerability period which can be abused to trigger Blood Donation Machines and Devil Beggars without losing health by placing a portal just next to it, teleporting, and touching the Donation Machine or Beggar in the same move. This trick is particularly useful for The Lost. The teleportation trick can also be used to escape Curse Rooms without taking damage.
Portals will stay even if the item is dropped or changed.
The item can prove useful in close quarters combat, allowing the player to attack one side, then dodge attacks and jump to the other side of the room to attack the enemies on that side.
Upon entering a new floor, the previously placed portals will disappear.
If Curse of the Maze is active, using portals placed between different rooms may result in a random destination. Two portals in the same room work reliably.
If room contents are randomized by the curse, it's possible for the portals to end up completely surrounded or even inside rocks or pits. If Isaac can't move to safety, the run can be quit and resumed to be placed at a door.
On Downpour II, Ventricle Razor cannot be used to teleport between the normal and mirror world.
This item can be useful to exit Mom's boss room to start the Ascent, as long as you use it at least once before entering the boss room.
Car Battery: Renders the item useless, as both portals are placed at the same time where the item is activated.
A ventricle is a hollow part in an organ.
The colors of the portals are a reference to the Portal Gun from the Portal series, whose portals share the same colors and functionality.
If the animation of entering a portal created by Ventricle Razor is forcibly cancelled, then the player will be unable to fire tears and collide with any non-grid entities (including trapdoors). This essentially renders the player immune to enemy attacks, hence enabling exploits using alternate offense methods (e.g. orbitals). Exiting and continuing the run restores the collision circle and the ability to fire tears.