  As a considerable investment of time from various telescope facilities were
dedicated toward studying the Spiderweb protocluster at $z=2.2$, it so far
remains one of the most extensively studied protocluster. We report here the
latest results in this field, adding a new dimension to previous research on
cluster formation at high redshift. Previous studies have reported a
significant overdensity ($\delta\sim10$) of massive H$\alpha$ (+ [Nii])
-emitting galaxies in 3700 comoving Mpc$^3$. Many of these were previously
considered to be dusty, actively star-forming galaxies, given their rest-frame
optical and infrared features. However, this study argues that a third of them
are more likely to be "passively-evolving" galaxies with low-luminosity active
galactic nuclei (AGNs) rather than star-forming galaxies, given the
multi-wavelength spectral energy distribution (SED) fitting including an AGN
component. For their SED-based star formation rates to be valid, bulk of their
H$\alpha$ + [Nii] emission should come from the central AGNs. This difference
in interpretation between this work and past studies, including ours, is
particularly supported by the recent deep Chandra X-ray observation.
Furthermore, we have spectroscopically confirmed a quiescent nature for one of
these AGNs, with its multiple stellar absorption lines but also low ionisation
emission lines. This important update provides new insights into the role of
AGNs in forming the cluster red sequence observed in the present-day universe.
