Ibbit is an entity referred to as a dolphin, with it's whole purpose being teleporting you to the scary little place.
Ibbit looks similar to Bibbit being another block with two, now fully red legs, but now with the body being more cube-like. It's body is fully black, with the word "SCARY" written on there.
Ibbit is neutral, meaning it won't hurt you if you won't hurt them. Walking up to Ibbit in the Overworld will result in you being teleported to the scary little place dimension.
Upon spawning, the message "another dolphin is nearby" will be sent. Nothing drops from Ibbit.
Ibbit viewed in Blockbench.