Horned Treehopper
Identified as Lubra spinicornis on Bowerbird by Tony D.: "I can't answer the purpose of the horns, but I believe this one falls within Lubra spinicornis, a species where the horns are very produced and variable but generally adorned with a spine on outer side. The horns can be convergent or divergent : https://biodiversity.org.au/afd/taxa/Lubra_spinicornis"