  Extreme high-energy peaked BL Lac objects (EHBLs) are a new emerging class of
blazars. The typical two-hump structured spectral energy distribution (SED) is
shifted to higher energies with respect to other more established classes of
blazars. Multi-wavelength observations allow us to constrain their synchrotron
peak in the medium and hard X-ray bands. Their gamma-ray emission dominates
above the GeV gamma-ray band, and in some objects it extends up to several TeV
(e.g. 1ES 0229+200). Their hard TeV spectrum is also interesting for the
implications on the extragalactic background light indirect measurements, the
intergalactic magnetic field estimate, and the possible origin of extragalactic
high-energy neutrinos. Up to now, only a few objects have been studied in the
TeV gamma-ray range. In this contribution, we will present the new detection of
the EHBL object PGC 2402248, recently discovered in TeV gamma rays with the
MAGIC telescopes. The analysis results of a set of multi-wavelength
simultaneous observations up to the VHE gamma-ray band provide the broad-band
SED of the blazar, which will be used to probe different emission models. Given
the extreme characteristics of this blazar, constraints on the physical
parameters within the framework of leptonic and hadronic models are derived.
