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We present optical imaging and spectroscopy of supernova (SN) LSQ13fn, a typeII supernova with several hitherto-unseen properties. Although it initiallyshowed strong symmetric spectral emission features attributable to\ion{He}{ii}, \ion{N}{iii}, and \ion{C}{iii}, reminiscent of some interactingSNe, it transitioned into an object that would fall more naturally under a typeII-Plateau (IIP) classification. However, its spectral evolution revealedseveral unusual properties: metal lines appeared later than expected, wereweak, and some species were conspicuous by their absence. Furthermore, the linevelocities were found to be lower than expected given the plateau brightness,breaking the SNe~IIP standardised candle method for distance estimates. Wefound that, in combination with a short phase of early-timeejecta-circumstellar material interaction, metal-poor ejecta, and a largeprogenitor radius could reasonably account for the observed behaviour.Comparisons with synthetic model spectra of SNe~IIP of a given progenitor masswould imply a progenitor star metallicity as low as 0.1\,Z$_{\odot}$. LSQ13fnhighlights the diversity of SNe~II and the many competing physical effects thatcome into play towards the final stages of massive star evolution immediatelypreceding core-collapse.

LSQ13fn: A type II-Plateau supernova with a possibly low metallicity progenitor that breaks the standardised candle relation