  We present the photometric and spectroscopic evolution of the Type II
supernova (SN II) SN 2017ivv (also known as ASASSN-17qp). Located in an
extremely faint galaxy (M$_r=-10.3$ mag), SN 2017ivv shows an unprecedented
evolution during the two years of observations. At early times, the light curve
shows a fast rise ($\sim6-8$ days) to a peak of ${\rm M}^{\rm max}_{g}= -17.84$
mag, followed by a very rapid decline of $7.94\pm0.48$ mag per 100 days in the
$V-$band. The extensive photometric coverage at late phases shows that the
radioactive tail has two slopes, one steeper than that expected from the decay
of $^{56}$Co (between 100 and 350 days), and another slower (after 450 days),
probably produced by an additional energy source. From the bolometric light
curve, we estimated that the amount of ejected $^{56}$Ni is $\sim0.059\pm0.003$
M$\odot$. The nebular spectra of SN 2017ivv show a remarkable transformation
that allows the evolution to be split into three phases: (1) H$\alpha$ strong
phase ($<200$ days); (2) H$\alpha$ weak phase (between 200 and 350 days); and
(3) H$\alpha$ broad phase ($>500$ days). We find that the nebular analysis
favours a binary progenitor and an asymmetric explosion. Finally, comparing the
nebular spectra of SN 2017ivv to models suggests a progenitor with a zero-age
main-sequence mass of 15 -- 17 \Msun.
