Dubbed "Programming from Hell" and specially designed with the view that programming should be hard. It has seven instructions, and the program must be encoded in a rather random way. It has not been proven Turing complete, and considering the automatic self-modification there is a good chance that it isn't. Indeed it is so difficult to program Malbolge that it took someone ages to finally write a "Hello, world" program.
Monumentally Useless Re-Iterative Execution Language. A language whose only means of control flow is to generate a new Muriel program as a string and then run it, without carrying forward the variables or returning to the original program. Creating a loop in Muriel is like writing a quine.