You need the ability to speak and walk around. When you see the mob on 'boss where' go to any cavern like rooms in that same zone and say xyzzy in each until he appears.
'Xyzzy' you say. *Floof!* A gnarled, gnobbly little sorceror appears directly before you. 'You rang?' a gnarled, gnobbly little sorceror asks. A gnarled, gnobbly little sorceror's voice echoes loudly throughout the area. A large stalactite is dislodged from the ceiling, narrowly missing a gnarled, gnobbly little sorceror! A gnarled, gnobbly little sorceror raises a quizzical eyebrow at you. You must have confused him.Attack and kill, dies in 1 hit. Everyone in form gets bosskill, whomever lands the killing blow also gets the mark of Xyzzy
Standard boss loot
A gnarled, gnobbly little sorceror is burned on the torso with your acid causing lethal damage. For finding and murdering the secret of Xyzzyy, the Powers have granted thee a Mark. You have gained the Mark of Xyzzy! You gain 41 practices! A gnarled, gnobbly little sorceror has been slain! Your blood freezes as you hear a gnarled, gnobbly little sorceror's death cry. You receive 0 archon points. Tyche has killed a new boss, a gnarled, gnobbly little sorceror. You have killed a new boss, a gnarled, gnobbly little sorceror. You have killed 22 bosses since your last PK. You gain 101 archon points! You gain 1 quest point! A gnarled, gnobbly little sorceror collapses lifeless to the ground. The severed head of a gnarled, gnobbly little sorceror falls to the ground. You take failsafe insurance from the Commissioner of Murder. Failsafe insurance from the Commissioner of Murder emits a bright flare of white light as it binds with you. You take a trinket traded from the Glyph. A trinket traded from the Glyph emits a bright flare of white light as it binds with you. You take an irukere ifa. An irukere ifa emits a bright flare of white light as it binds with you. You take 1,464 gold coins. You split 1,464 gold coins. Your share is 488 gold coins. You take 2 of a trophy that looks like the boss, a gnarled, gnobbly little sorceror [2018 Edition] from the corpse of a gnarled, gnobbly little sorceror. You take the fragmented remnants of a powerful artifact from the corpse of a gnarled, gnobbly little sorceror. The Powers give you one gold coin for your sacrifice of the corpse of a gnarled, gnobbly little sorceror.