* RST instructions are just a CALL instruction to a fixed address baked in the instruction itself.
* Despite what the syntax of the instructions JP (HL/IX/IY) suggests, PC will be loaded with the contents of the register itself, not the indexed value. Those instructions should be understood as JP HL/IX/IY.
* The instructions LD A,A, LD B,B, LD C,C, LD D,D, LD E,E, LD H,H and LD L,L are useless. Their existence is just a side effect of how instructions are encoded as opcodes in the CPU. However, some Game Boy emulators (such as BGB) interpret LD B,B as a breakpoint, or LD D,D as a debug message.
* While the syntax of the 8-bit ADD, ADC and SBC instructions all explicitly mention the A register, the SUB instruction does not mention it.
* Arithmetic can only really be done on the A register.