We report the discovery of a mysterious giant \(H_{\alpha}\) blob that is \(\sim 8\) kpc away from the main MaNGA target 1-24145, one component of a dry galaxy merger, identified in the first-year SDSS-IV MaNGA data. The size of the \(H_{\alpha}\) blob is \(\sim\) 3-4 kpc in radius, and the \(H_{\alpha}\) distribution is centrally concentrated. However, there is no optical continuum counterpart in deep broadband images reaching \(\sim\)26.9 mag arcsec\(^{-2}\) in surface brightness. We estimate that the masses of ionized and cold gases are \(3.3 \times 10^{5}\) \(\rm M_{\odot}\) and \(< 1.3 \times 10^{9}\) \(\rm M_{\odot}\), respectively. The emission-line ratios indicate that the \(H_{\alpha}\) blob is photoionized by a combination of massive young stars and AGN. Furthermore, the ionization line ratio decreases from MaNGA 1-24145 to the \(H_{\alpha}\) blob, suggesting that the primary ionizing source may come from MaNGA 1-24145, likely a low-activity AGN. Possible explanations of this \(H_{\alpha}\) blob include AGN outflow, the gas remnant being tidally or ram-pressure stripped from MaNGA 1-24145, or an extremely low surface brightness (LSB) galaxy. However, the stripping scenario is less favoured according to galaxy merger simulations and the morphology of the \(H_{\alpha}\) blob. With the current data, we can not distinguish whether this \(H_{\alpha}\) blob is ejected gas due to a past AGN outburst, or a special category of `ultra-diffuse galaxy' (UDG) interacting with MaNGA 1-24145 that further induces the gas inflow to fuel the AGN in MaNGA 1-24145.