Decapping scavenger enzyme that catalyzes the cleavage of a residual cap structure following the degradation of mRNAs of the 3'->5' exosome-mediated mRNA decay pathway. Hydrolyzes cap analog structures like 7-methylguanosine nucleoside triphosphate (m7GpppG) and tri-methyl guanosine nucleoside triphosphate (m3(2,2,7)GpppG) with up to 2 nucleotide substrates (small capped oligoribonucleotides) and specifically releases 5'-phosphorylated RNA fragments and 7-methylguanosine monophosphate (m7GMP). Does not hydrolyze unmethylated cap analog (GpppG) and shows no decapping activity on intact m7GpppG-capped mRNA molecules. Does not hydrolyze 7-methylguanosine diphosphate (m7GDP) and tri-methylguanosine diphosphate (m3(2,2,7)GDP) to m(7)GMP and m3(2,2,7)GMP, respectively (PubMed:15383679, PubMed:22985415). May also play a role in the 5'->3 mRNA decay pathway; m7GDP, the downstream product released by the 5'->3' mRNA mediated decapping activity, may be also converted by dcs-1 to m7GMP. Binds to m7GpppG and strongly to m7GDP. a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-ribonucleoside in mRNA + H2O = a 5'-end diphospho-ribonucleoside in mRNA + 2 H(+) + N(7)-methyl-GMP a 5'-end (N(2),N(2),N(7)-trimethyl 5'-triphosphoguanosine)-(ribonucleoside) in mRNA + H2O = (N(2),N(2),N(7))-trimethyl-GMP + a 5'-end diphospho-ribonucleoside in mRNA + 2 H(+) The hydrolytic product 7-methylguanosine diphosphate (m7GDP) efficiently inhibits the decapping scavenger activity and acts as a competitive inhibitor in vitro. Belongs to the HIT family.