Many theories beyond the Standard Model have been proposed to address several of its shortcomings. Some of these beyond-the-Standard-Model extensions predict new particles or interactions directly accessible at the Large Hadron Collider, but which would leave unconventional signatures in the ATLAS detector. These unconventional signatures require special techniques and reconstruction algorithms that, once developed, enable analysers to perform unique searches for new physics. These proceedings cover several such searches using the Run-2 dataset.