  SN\,2020qlb (ZTF20abobpcb) is a hydrogen-poor superluminous supernova
(SLSN-I) that is among the most luminous (maximum M$_{g} = -22.25$ mag) and
that has one of the longest rise times (77 days from explosion to maximum). We
estimate the total radiated energy to be $>2.1\times10^{51}$ erg. SN\,2020qlb
has a well-sampled light curve that exhibits clear near and post peak
undulations, a phenomenon seen in other SLSNe, whose physical origin is still
unknown. We discuss the potential power source of this immense explosion as
well as the mechanisms behind its observed light curve undulations. We analyze
photospheric spectra and compare them to other SLSNe-I. We constructed the
bolometric light curve using photometry from a large data set of observations
from the Zwicky Transient Facility (ZTF), Liverpool Telescope (LT), and Neil
Gehrels Swift Observatory and compare it with radioactive, circumstellar
interaction and magnetar models. Model residuals and light curve polynomial fit
residuals are analyzed to estimate the undulation timescale and amplitude. We
also determine host galaxy properties based on imaging and spectroscopy data,
including a detection of the [O III]$\lambda$4363, auroral line, allowing for a
direct metallicity measurement. We rule out the Arnett $^{56}$Ni decay model
for SN\,2020qlb's light curve due to unphysical parameter results. Our most
favored power source is the magnetic dipole spin-down energy deposition of a
magnetar. Two to three near peak oscillations, intriguingly similar to those of
SN\,2015bn, were found in the magnetar model residuals with a timescale of
$32\pm6$ days and an amplitude of 6$\%$ of peak luminosity. We rule out
centrally located undulation sources due to timescale considerations; and we
favor the result of ejecta interactions with circumstellar material (CSM)
density fluctuations as the source of the undulations.
