What is the stuff called takhash that was used in the wilderness in #exodus 25:5, 26:14 and other places in Torah? Nobody knows for sure. It's been translated as the skin of porpoise, goat, dugong, badger, and even unicorn. Some believe that the takhash of the Tabernacle's outer covering was multi-colored. Something like Joseph's coat, perhaps?

In my opinion (based on non-scholarly Internet research) the most plausible meaning is a shallow-water, oceanic mammal, like a dugong or seal. Narwhal, badger, and unicorn seem extremely unlikely and porpoise slightly less unlikely.