According to the official results of the Polish parliamentary election, the Law and Justice party (PiS) has won majority in the Sejm (the lower house), but lacks majority in the Senate (the upper house): it has 49 out of 100 senators (including one PiS-aligned independent senator). Such a situation is unprecedented in the history of Polish democracy.
An opinion of the Senate can be rejected by the Sejm:
an opinion of the Senate on an act passed by the Sejm may by rejected by an absolute majority of votes cast by at least half of the statutory number of deputies
Does the Senate have any prerogatives that can make PiS unable to form a functioning government without a coalition? If not, does it have any prerogatives that can stop PiS's controversial Orbán-style reforms? Is it likely that PiS manages to buy two opposition senators' votes in exchange for some favours?