The peculiarity of Malbolge is that it was designed to be the worst possible programming language (i.e., the most difficult to use). As such it is an Esoteric programming language.
The difficulty of programming in Malbolge is evidenced by the fact that the first Malbolge program ever written came to birth 2 years after the invention of the language! Moreover, it was not written by a human being; instead, it was generated by a beam search algorithm designed by Andrew Cooke [1] and implemented in Lisp.
According to the documentation that comes with Malbolge, it is designed to emulate a simple trinary machine. This, in and of itself, isn't difficult to handle; what makes Malbolge truly difficult is that the compiler takes a character, finds the ASCII value, applies modulus 92 on it, and then uses that as its command. It then increments a counter which it will add to future values.
There is some argument that Malbolge is not Turing complete, i.e. it cannot be used to program a computer to do everything. Due to the difficulty inherent in implementing a program in Malbolge, definitive proof that it is, indeed, Turing complete may never come.
Hello World in Malbolge
This Malbolge program displays "HEllO WORld".
(=<`$9]7<5YXz7wT.3,+O/o'K%$H"'~D|#z@b=`{^Lx8%$Xmrkpohm-kNi;
gsedcba`_^]\\[ZYXWVUTSRQPONMLKJIHGFEDCBA@?>=<;:9876543s+O