After daydreaming the concept I recently unleashed this idea on my players. The specific mechanics were thrown together on the spot but everyone had a good time. The treasure golem is a rewarding encounter for it's theme and spectacle, not it's mechanical depth. However it has a few tricks up it's sleeve.

This could be used as a the primary or final means of defence. If it's the primary foe in a location then you could make it more difficult or complex mechanically. If it's the final enemy after a long slog through a dungeon or following a dragon fight then perhaps tone down the difficulty for a weakened party. the story of the battle will be just as rewarding as the treasure itself. I include some suggested alterations at the end.

• Sandman from Spiderman
• cone attack that applies slow
• Can charge over enemies, also applying slow
• As it takes damage it reduces in size and damage output.

Optional to have the creature split and combine as needed for drama.