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We present optical observations of the Type I superluminous supernova(SLSN-I) SN2017dwh at $z\!\approx\!0.13$, which reached $M_{i}\!\approx\!-21$mag at peak. Spectra taken a few days after peak show an unusual and strongabsorption line centered near 3200\AA\ that we identify with Co II, suggestinga high fraction of synthesized $^{56}$Ni in the ejecta. By $\sim\!1$ monthafter peak, SN2017dwh became much redder than other SLSNe-I, instead stronglyresembling broad-lined Type Ic supernovae (Ic-BL SNe) with clear suppression ofthe flux redward of $\sim\!5000$ \AA, providing further evidence for a largemass of Fe-group elements. Late-time upper limits indicate a $^{56}$Ni mass of$\lesssim 0.6$ M$_\odot$, leaving open the possibility that SN2017dwh produceda $^{56}$Ni mass comparable to SN1998bw ($\approx\!0.4$ M$_\odot$). Fitting thelight curve with a combined magnetar and $^{56}$Ni model using ${\tt MOSFiT}$,we find that the light curve can easily accommodate such masses withoutaffecting the inferred magnetar parameters. We also find that SN2017dwhoccurred in the least-luminous detected host galaxy to date for a SLSN-I, with$M_{B} = -13.5$ mag and an implied metallicity of $Z\!\sim\!0.08$ $Z_\odot$.The spectral properties of SN2017dwh provide new evidence linking SLSNe-I withType Ic-BL SNe, and in particular the high Fe-group abundance may be due toenhanced $^{56}$Ni production or mixing due to asphericity. Finally, we findthat SN2017dwh represents the most extreme end of a correlation betweencontinuum shape and Co II absorption strength in the near-peak spectra ofSLSNe-I, indicating that Fe-group abundance likely accounts for some of thevariation in their spectral shapes.

A Hydrogen-Poor Superluminous Supernova with Enhanced Iron-Group Absorption: A New Link Between SLSNe and Broad-Lined Type Ic SNe