Erasmus was previously on the books of Mthatha Bucks, who were relegated this past season to the ABC Motsepe League where Mashigo plied his trade for Swallows FC.
"We have signed Tshepo Mashigo and Mpho Erasmus," Natal Rich Boys chairman Sifiso Biyela tells KickOff.com.
Erasmus, who was an early contender for the NFD Golden Boot before losing his scoring touch in January, ended up netting 11 times in 28 league matches for Amathol'mnyana.
Mashigo, who was loaned by Cape Town All Stars to the Dube Birds, garnered attention when he scored an equaliser against Maritzburg United in the Nedbank Cup Last-32 in February at Dobsonville Stadium. The Team of Choice went on to win 3-1.
He scored four goals in six appearances for All Stars before joining Swallows after both sides agreed in principle that the Birds would be purchasing their NFD status.
As previously revealed by this website, the club will coached by Brandon Truter, who steered Igugu Lekapa this past season.