  Planetary systems formed in clusters may be subject to stellar encounter
flybys. Here we create a diverse range of representative planetary systems with
different orbital scales and planets' masses and examine encounters between
them in a typical open cluster. We first explore the close-in multi-super earth
systems $\lesssim0.1$ au. They are resistant to flybys in that only ones inside
a few au can destabilise a planet or break the resonance between such planets.
But these systems may capture giant planets onto wide orbits from the intruding
star during distant flybys. If so, the original close-in small planets' orbits
may be tilted together through Kozai--Lidov mechanism, forming a ``cold''
system that is significantly inclined against the equator of the central host.
Moving to the intermediately-placed planets around solar-like stars, we find
that the planets' mass gradient governs the systems' long-term evolution
post-encounter: more massive planets have better chances to survive. Also, a
system's angular momentum deficit, a quantity describing how eccentric/inclined
the orbits are, measured immediately after the encounter, closely relates to
the longevity of the systems -- whether or not and when the systems turn
unstable in the ensuing evolution millions of years post-encounter. We compare
the orbits of the surviving planets in the unstable systems through (1) the
immediate consequence of the stellar fly or (2) internal interplanetary
scattering long post-encounter and find that those for the former are
systematically colder. Finally, we show that massive wide-orbit multi-planet
systems like that of HR 8799 can be easily disrupted and encounters at a few
hundreds of au suffice.
