We present comprehensive observations and analysis of the energetic H-stripped SN 2016coi (a.k.a. ASASSN-16fp), spanning the $gamma$-ray through optical and radio wavelengths, acquired within the first hours to $sim$420 days post explosion. Our campaign confirms the identification of He in the SN ejecta, which we interpret to be caused by a larger mixing of Ni into the outer ejecta layers. From the modeling of the broad bolometric light curve we derive a large ejecta mass to kinetic energy ratio ($M_{rm{ej}}sim 4-7,rm{M_{odot}}$, $E_{rm{k}}sim 7-8times 10^{51},rm{erg}$). The small [ion{Ca}{ii}] lamlam7291,7324 to [ion{O}{i}] lamlam6300,6364 ratio ($sim$0.2) observed in our late-time optical spectra is suggestive of a large progenitor core mass at the time of collapse. We find that SN 2016coi is a luminous source of X-rays ($L_{X}>10^{39},rm{erg,s^{-1}}$ in the first $sim100$ days post explosion) and radio emission ($L_{8.5,GHz}sim7times 10^{27},rm{erg,s^{-1}Hz^{-1}}$ at peak). These values are in line with those of relativistic SNe (2009bb, 2012ap). However, for SN 2016coi we infer substantial pre-explosion progenitor mass-loss with rate $dot M sim (1-2)times 10^{-4},rm{M_{odot}yr^{-1}}$ and a sub-relativistic shock velocity $v_{sh}sim0.15c$, in stark contrast with relativistic SNe and similar to normal SNe. Finally, we find no evidence for a SN-associated shock breakout $gamma$-ray pulse with energy $E_{gamma}>2times 10^{46},rm{erg}$. While we cannot exclude the presence of a companion in a binary system, taken together, our findings are consistent with a massive single star progenitor that experienced large mass loss in the years leading up to core-collapse, but was unable to achieve complete stripping of its outer layers before explosion.
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