In time a dark passageway terminates before great stone doors bound in gold. The doors aren't very impressive for a Final Boss fight by the standards of larger dungeons, but Bella is unlikely to have personally been inside any dungeons with doors more impressive than that.
The Slimes escort her in. A lone torch lights at the center of the room, as she enters, revealing a raised black marble plinth at the room's center. The plinth is empty. In the lone torch's light it is barely possible for Bella's dark-adjusted eyes to see that there are smaller golden doors at the other side of the room.
The Mutant Chameleon Metallic Slime slurps its way onto the raised plinth, resuming its place as the Final Boss of the dungeon. It then stands there, motionless and quivering; and slowly turns translucent, revealing a brighter core inside itself.
It raises a tentacle and reforms it into hands, one final time.
<You must slay - the final boss - for the final doors to open. There is no other way. Cleave the slime's core. It will revive in time.>