The character has 2 fully functional brains that work in concert. The mutant receives a bonus of 10% to all technology rolls, and the character receives one extra random mental mutation that belongs to the extra brain. Both brains have identical WIL. Having two brains also helps to protect the mutant from mental attacks. Whenever the character is the subject of a mental attack, the attacker must successfully attack each brain.
Note that a character with two brains may or may not have two heads. One brain may be located in an unexpected part of the body, or as part of a small, sickly or undeveloped conjoined twin.