2010-11: Melvin Nyffeler appeared in two games with ZSC's U20 team in Switzerland's Elite Junior B league as a 16-year-old and played one game for the GC Kusnacht U20 club while skating for the ZSC U17 team. He played five games for Switzerland's U17 team and had a 4.67 goals against and .855 save percentage.
2011-12: Nyffeler played two games for Switzerland's U18 team at the 2011 Ivan Hlinka Memorial Tournament in August before returning to Zurich to skate for the GCK Lions in the Junior Elite League. He ended the season competing for Swtizerland's U18 team in the 2012 World Junior Championship. Nyffeler was 18-2 with three shutouts and had a 1.65 goals against in 20 regular season games — tops in the Swiss junior elite league — and in six playoff games was 5-1 with 1on shutout and posted a 1.85 goals against. The Lions captured the elite league championship. Nyffeler had a 2.00 goals against and .937 save percentage in two games at the Ivan Hlinka tournament, sharing time with Robin Kuonen, and was 2-3 in five games for Switzerland at the WJC with a 3.95 goals against and .867 save percentage.
2012-13: Nyffeler made his pro hockey debut in Switzerland, skating in 19 games for GC Kusnacht in Switzerland's National B league, and represented Switzerland in a pair of international tournaments. He had a 2.79 goals against in 16 regular season games and a 4.05 goals against in three playoff games for the Lions. Nyffeler played for the club's Swiss champion junior team. He was 2-2-2 with a 3.42 goals against in six regular season games and in 10 playoff games was 7-2; posting a 2.19 goals against. Nyfeller played three games for Switzerland's U19 team at the World Junior A Challenge, posting a 2.18 goals against and .925 save percentage. Expected to back up Luca Boltshauser, Nyffeler emerged as one of the heroes for Switzerland's U20 team at the 2013 World Junior Championship. The Swiss reached the playoff round and finished sixth; going 1-3 in the preliminary round. Nyffeler was 0-4, with three losses in overtime and a shootout loss to Russia in the quarterfinals. He had a 3.67 goals against and .902 save percentage. Nyffeler was ranked seventh amongst European goaltenders in Central Scouting's final rankings prior to the 2013 NHL Draft but was not selected.
2013-14: Nyffeler made his debut in Switzerland's National A league — appearing in 11 games for the Marc Crawford-coached ZSC club — splitting the year between ZSC and the B league's Kusnacht Lions. He played for Switzerland in the 2013 World Junior Championship and was with the GCK Lions for the junior playoffs. Nyffeler was 7-2-1 with two shutouts and had a 1.25 goals against and .960 save percentage in 11 NLA games. In 23 NLB games with Kusnacht he was 11-8-4 with one shutout and had a 2.52 goals against. Nyffeler was 2-2 in four games at the WJC with a 3.45 goals against and .880 save percentage. Switzerland lost 4-1 to Canada in the quarterfinals. He was ranked eighth amongst European goaltenders in Central Scouting's mid-term rankings prior to the 2014 NHL Draft.