Insolent Basalt shadows appear on B1F and B2F of the Secret Laboratory within the Midnight Channel. They will attack normally until injured, at which point they'll use their Last Resort skill. Upon being defeated, they may drop the Insolence Steel material. Selling 4 Insolence Steel at Daidara will unlock the Midare Hamon sword for the protagonist for sale in the shop.
In Golden, it may appear from B1F to B4F. It may also drop Bloodstone.