Together with other emerging tobacco products, snuff/snus is banned in Singapore with effect from 1 August 2016. From this date it is prohibited to bring snuff/snus to Singapore.
The rules for tobacco and snuff/snus are only applicable when entering Singapore, they are not applicable in the transit area at the airport.
For more information, see press release from The Ministry of Health here.
Until 1 August 2016, all tobacco products, including snuff/snus, must be declared at Singapore Customs upon arrival. The duty rates are listed here.
You are strongly encouraged to visit the web site of Singapore Customs, since the rules are subject to changes and are quite strict.