  We present photometric and spectroscopic observations of the 03fg-like type
Ia supernova (SN Ia) ASASSN-15hy from the ultraviolet (UV) to the near-infrared
(NIR). ASASSN-15hy shares many of the hallmark characteristics of 03fg-like SNe
Ia, previously referred to as "super-Chandrasekhar" SNe Ia. It is bright in the
UV and NIR, lacks a clear i-band secondary maximum, shows a strong and
persistent C II feature, and has a low Si II $\lambda$6355 velocity. However,
some of its properties are also extreme among the subgroup. ASASSN-15hy is
under-luminous (M$_{B,peak}=-19.14^{+0.11}_{-0.16}$ mag), red
($(B-V)_{Bmax}=0.18^{+0.01}_{-0.03}$ mag), yet slowly declining
($\Delta{m_{15}}(B)=0.72 \pm 0.04$ mag). It has the most delayed onset of the
i-band maximum of any 03fg-like SN. ASASSN-15hy lacks the prominent H-band
break emission feature that is typically present during the first month past
maximum in normal SNe Ia. Such events may be a potential problem for
high-redshift SN Ia cosmology. ASASSN-15hy may be explained in the context of
an explosion of a degenerate core inside a non-degenerate envelope. The
explosion impacting the non-degenerate envelope with a large mass provides
additional luminosity and low ejecta velocities. An initial deflagration
burning phase is critical in reproducing the low $^{56}$Ni mass and luminosity,
while the large core mass is essential in providing the large diffusion time
scales required to produce the broad light curves. The model consists of a
rapidly rotating 1.47 $M_{\odot}$ degenerate core and a 0.8 $M_{\odot}$
non-degenerate envelope. This "deflagration core-degenerate" scenario may
result from the merger between a white dwarf and the degenerate core of an
asymptotic giant branch star.
