Molten Ender is the liquid essence of Endermen's teleportation ability. It is obtained by melting Ender Pearls in a Magma Crucible. It can be transported through waterproof pipes and is used in a Liquid Transposer to fill Empty Tesseract Frames. Each Empty Tesseract Frame requires 1000mB Molten Ender (4 Ender Pearls) to become an Unattuned Tesseract.
Molten Ender can be stored in buckets and placed in the world where it flows like other liquids. If you touch the liquid, you will be randomly teleported a short random distance and direction, even through walls, ceilings, or floors. Use near lava often proves comical and disastrous.