This thing was made for a fish/mermaid carnival-costume.
It should represent the dorsal fin of sea-fish (a picture of a Mahi-mahi was used as an example for modelling proportions).
print both half's (one half fit's on a 200x200mm heatbed)
take for example Revell plastics glue for bringing them together (use m3-screws for perfect and easy positioning)
paint the crown (we used blue an green color : Revell colors (50); (61); (752))
take care that your hairband fits in the semicircular cutout for easy fixing it on your head (otherwise it takes some rework)
or fix it with hairclips at the m3-holes