You can use the North East Line or the Circle Line of the Singapore MRT system to travel to NEX (Serangoon) by MRT.
You can get off the North East Line at Serangoon MRT stop and exit in the direction of NEX if you're traveling there. It is simple to get to the mall even in inclement weather because it is linked to the station by a covered walkway.
If you're traveling on the Circle Line, you can exit at Serangoon MRT station and head in an opposite direction, toward NEX. You can follow the indications to the appropriate exit because the Circle Line platform is situated beneath the North East Line platform at Serangoon station.
Both routes provide easy access to NEX, a sizable shopping center in Singapore's Serangoon district.