This is a Halloween themed drinking game that requires a little concentration. Players take turns counting up from 1, i.e. the first person says "1", the second person says "2", etc. However, players must say "monster" on numbers divisible by 3, "mash" on numbers divisible by 5 and "monster mash" on numbers divisible by both. As soon as someone messes up (and this will happen quickly and often) then they must take a sip of their drink. Make sure at least one person in the group isn't terrible at maths, or no one will know when anyone's made a mistake.