Buster's drop table was never updated to the new equipment system, which means he may still drop the unique Purple-quality item Grey Goo.
When Buster is originally found, he appears to be a training mannequin, completely unable to take damage. Attacking him repeatedly will cause him to fight back, using a Might-based combat build. (It is unknown as to whether the exact trigger is based on damage dealt, attacks done, or simply time; for a solo character at level 40, it took just over five minutes to trigger.)
