  We present the discovery of Kepler-129 d ($P_{d}=7.2^{+0.4}_{-0.3}$ yr,
$m\sin i_{d}=8.3^{+1.1}_{-0.7}\ \rm M_{Jup}$, $ e_{d}=0.15^{+0.07}_{-0.05} $)
based on six years of radial velocity (RV) observations from Keck/HIRES.
Kepler-129 also hosts two transiting sub-Neptunes: Kepler-129 b ($P_{b}=15.79$
days, $r_{b}=2.40\pm{0.04}\ \rm{R_{\oplus}}$) and Kepler-129 c ($P_{c}=82.20$
days, $r_{c}=2.52\pm{0.07}\ \rm{R_{\oplus}}$) for which we measure masses of
$m_{b}<20\ \rm{M_{\oplus}}$ and $m_{c}=43^{+13}_{-12}\ \rm{M_{\oplus}}$.
Kepler-129 is an hierarchical system consisting of two tightly-packed inner
planets and an external companion whose mass is close to the deuterium burning
limit. In such a system, two inner planets precess around the orbital normal of
the outer companion, causing their inclinations to oscillate with time. Based
on an asteroseismic analysis of Kepler data, we find tentative evidence that
Kepler-129 b and c are misaligned with stellar spin axis by $\gtrsim 38$ deg,
which could be torqued by Kepler-129 d if it is inclined by $\gtrsim 19$ deg
relative to inner planets. Using N-body simulations, we provide additional
constraints on the mutual inclination between Kepler-129 d and inner planets by
estimating the fraction of time during which two inner planets both transit.
The probability that two planets both transit decreases as their misalignment
with Kepler-129 d increases. We also find a more massive Kepler-129 c enables
the two inner planets to become strongly coupled and more resistant to
perturbations from Kepler-129 d. The unusually high mass of Kepler-129 c
provides a valuable benchmark for both planetary dynamics and interior
structure, since the best-fit mass is consistent with this $\rm{2.5\
R_{\oplus}}$ planet having a rocky surface.
