Comparison between medium resolution spectra of AT 2021blu, NGC4490-2011OT1 (Smith et al. 2016), AT 2020hat (Pastorello et al. 2021a), and AT 2019zhd (Pastorello 2021b) obtained during the plateau or the red peak phase. Top panel: close-up view of the region between 4400 and 5500 Å. Middle panel: view of the region from 5500 to 6500 Å. Bottom panel: View of the region from 6500 to 7570 Å. Despite the objects are different, most of narrow metal lines are observed in all the spectra.