The NA48/2 experiment at CERN collected a large sample of
charged kaon decays into final states with multiple charged
particles in 2003-2004. An upper limit of $8.6 \times 10^{-11}$ at
90~$\%$~CL is set on the branching ratio of the lepton number violating
decay $K^\pm \rightarrow \pi^{\mp} \mu^{\pm} \mu^{\pm}$. Searches
for two-body resonances like heavy neutral
leptons and inflatons in the $K^\pm \rightarrow \pi \mu \mu$ decays
in the accessible range of masses and lifetimes are also presented.