Tar Pit

A tar pit: an irregular pool 4.0 x 3.0 m of black tar inside a low crusted rim of tar-soaked umber seep, flat base at y=0 to sit in the terrain's tar-pit basin, its surface glossy with slow modelled swells and a few sluggish bubbles; tar is its own zone.

风格：low-poly, flat-shaded vertex colors, no textures, 2 materials: the shared opaque one plus a distinct surface (glass, water or chrome), which stays its own mesh through mergeAssets rather than merging into the rest; shares palette and scale with its kit