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Abstract: The discovery of pulsating ultraluminous X-ray sources (PULXs) has revealed that accreting neutron stars can shine at extreme luminosities, well above their Eddington limit. This finding has caused a shift in the ULX paradigm and poses significant challenges to our understanding of the physics of accretion onto compact objects. Given their rarity, every new insight into their complex phenomenology can bring us closer to a deeper understanding of these sources. A possible way to find more PULXs is by searching the archives of X-ray missions with good imaging and timing capabilities using a data mining approach. In the process, serendipitous sources are always behind the corner. Both the study of PULXs and the search for new X-ray pulsators through data mining have defined the course of my PhD. I will report my discovery of mHz QPOs in the X-ray flux of the PULXs. These mHz QPOs could represent a signature of super-Eddington accretion. I will also talk about a new pulsar (likely a new candidate magnetar) I discovered in the Large Magellanic Cloud thanks to a data mining project aimed at searching for new pulsators in the XMM-Newton archive. Slides available here: https://www.ntnu.no/wiki/download/attachments/195538250/NTNU_seminar_Imbrogno.pdf?api=v2