  The second-order nonlinear Hall effect illuminates a frequency-doubling
transverse current emerging in quantum materials with broken inversion symmetry
even when time-reversal symmetry is preserved. This nonlinear response
originates from both the Berry curvature dipole and the chiral Bloch electron
skew scatterings, reflecting various information of the lattice symmetries,
band dispersions, and topology of the electron wavefunctions. Even though many
efforts have been put in detecting the nonlinear Hall effect in diverse
condensed matter systems, effective manipulation of the two principal
mechanisms in a single system has been lacking, and the reported response is
relatively weak. Here, we report effective manipulation of the nonlinear Hall
effect and realization of a colossal second-order Hall conductivity, $\sim500
{\mu}mSV^{-1}$, orders of magnitudes higher than the reported values, in AB-BA
stacked twisted double bilayer graphene. A Berry-curvature-dipole-dominated
nonlinear Hall effect, as well as its controllable transition to
skew-scattering-dominated response, is identified near the band edge. The
colossal response, on the other hand, is detected near the van Hove
singularities, mainly determined by the skew scattering of the chiral Bloch
electrons. Our findings establish electrically tunable moir\'e systems
promising for nonlinear Hall effect manipulations and applications.
