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tokens: evolution. The transition occurs at the same time as light curve evolves on to the linear tail. Similar evolution, across a similar time-scale, is seen in Type IIb SN 2008bo (Bianco et al. 2014 ), with the sole difference over the first 120 d being that SN 2008bo has an initial blueward evolution until ∼12 d after explosion that is not seen in SN 2018gjx. This blue/red/blue evolution is commonly seen in SE-SNe (Prentice et al. 2016 ). However, SNe with strong shock-cooling tails in their light curves (e.g. SNe 1993J, 2013df, 2016gkg; Richmond et al. 1994 ; Morales-Garoffolo et al. 2014 ; Tartaglia et al. 2017 ) evolve straight from blue to red at these early times, and it is to these that SN 2018gjx is most similar. Comparatively, SNe Ibn show great diversity in their colour evolution. SN 2015G is most like SN 2018gjx and is plotted using the estimated explosion date of 3 d prior to the discovery date (2015-03-23.778, but see Shivvers et al. 2017b , for a discussion on t exp ). SN 2006jc displays an inverted evolution to that of SN 2018gjx, and two other SNe Ibn LSQ13ddu (Clark et al. 2020 ) and SN 2014av (Pastorello et al. 2016 ), appear to follow the trend of blue to red, albeit from a bluer starting point. 3.2 Pseudo-bolometric and absolute <italic>r</italic>-band light curves An optical pseudo-bolometic light curve was constructed by converting the dereddened multicolour photometry to flux and building spectral energy distributions (SEDs) for each date. These SEDs were then integrated over 4000−10 000 Å, covering the effective range of the griz bandpasses and converted to pseudo-bolometric luminosity using a fixed luminosity distance of 35 Mpc. This method is described in more detail in Prentice et al. ( 2016 ). The pseudo-bolometric light curve of SN 2018gjx is shown in Fig. 4 in comparison with SNe IIb and SNe Ibn. It is a requirement of the bolometric light-curve methods that the transients are observed in BVRI, gri , or equivalent and while some interpolation and extrapolation can be done to account for missing data, we find that many SNe Ibn are only well-sampled in one or two bands, which limits our comparison sample. The peak luminosity of ∼1.4 × 10 42 erg s −1 places the first peak in a similar range to that of the SNe IIb that show shock-cooling tails. After this, the light-curve evolution diverges and fails to rise a second peak. It instead tracks the evolution of SN 2008bo, although with a steeper linear decline of ∼0.026 mag d −1 . The decline is steeper than for most SNe IIb (Prentice et al. 2019 ). Figure 4. Upper panel: The pseudo-bolometric light curve of SN 2018gjx compared with SNe IIb. The unusual SN IIb 2008bo has a remarkably similar light curve after 10 d. Lower panel: Absolute R / r LCs of SNe Ibn (squares) and SNe IIb (diamonds) in comparison with SN 2018gjx (black stars). Type Ibn SN 2015G (orange), Type IIb SN 2008bo (red), and Type IIb SN 2018ivc (gold) show similar evolution. The dramatic decline of SN 2006jc is