What's the strangest Assembler or Pseudo-Assembler you've ever encountered?

I wrote a Z-machine (Infocom's virtual text adventure interpreter) and it was quite an interesting interpretation of bytes:
- The first 3 bits of an instruction tell you the opcode category, the rest are the instruction
- The 2nd (and maybe 3rd) byte tell you in 2-Bit chunks the operand types.
- text is encoded in 5-Bit chunks, with special characters for CapsLock that double function as padding (if your text doesn't align with the 3 letters per 2 bytes).
- and of course there are 5 different versions that all work slightly differently (as in CapsLock becomes Shift or "this special character isn't in use anymore")