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We present photometric and spectroscopic observations of SN 2020bio, adouble-peaked Type IIb supernova (SN) discovered within a day of explosion,primarily obtained by Las Cumbres Observatory and Swift. SN 2020bio displays arapid and long-lasting initial decline throughout the first week of its lightcurve, similarly to other well-studied Type IIb SNe. This early-time emissionis thought to originate from the cooling of the extended outer hydrogen-rich(H-rich) envelope of the progenitor star that is shock heated by the SNexplosion. We compare SN 2020bio to a sample of other double-peaked Type IIbSNe in order to investigate its progenitor properties. Analytical model fits tothe early-time emission give progenitor radius ($\approx$ 100--1500 $R_\odot$)and H-rich envelope mass ($\approx$ 0.01--0.5 $M_\odot$) estimates that areconsistent with other Type IIb SNe. However, SN 2020bio displays severalpeculiarities, including: (1) weak H spectral features indicating a greateramount of mass loss than other Type IIb progenitors; (2) an underluminoussecondary light-curve peak that implies a small amount of synthesized $^{56}$Ni($M_{\text{Ni}}$ $\approx$ 0.02 $M_\odot$); and (3) low-luminosity nebular [OI] and interaction-powered nebular features. These observations are moreconsistent with a lower-mass progenitor ($M_{\text{ZAMS}} \approx$ 12$M_\odot$) that was stripped of most of its H-rich envelope before exploding.This study adds to the growing diversity in the observed properties of Type IIbSNe and their progenitors.

SN 2020bio: A Double-peaked, H-poor Type IIb Supernova with Evidence of Circumstellar Interaction