Won "Mafa" Sang-yeon began his career as the support for StarTale in March of 2012. StarTale played in Azubu The Champions Spring 2012 but they failed to make it through the group stage. At Azubu The Champions Summer 2012, StarTale actually made it out of groups but ended up losing in the quarterfinals 2-0 to NaJin Sword. StarTale disbanded in August with Mafa, Joker, and Ryu joining the new KT Rolster B roster.
KTB played in their first major tournament together at OLYMPUS Champions Winter 2012-2013 and ended in third place after losing two sets, 3-1 and 3-0, to Sword but beating Azubu Blaze 3-0. KTB didn't do as well in OLYMPUS Champions Spring 2013, losing 3-1 to MVP Ozone. A little later, KTB and their sister team, KT Rolster A, were renamed to the KT Rolster Bullets and the KT Rolster Arrows. HOT6iX Champions Summer 2013 was the breakout season of the Bullets, making the finals and playing one of the best series of League of Legends ever against SK Telecom T1. Unfortunately for the Bullets, they lost a close 3-2 set against SKT. The Bullets had enough circuit points to qualify for the Season 3 Korea Regional Finals but they met SKT again in the finals, this time losing 3-1. KTB missed the Season 3 World Championship even though they were considered the second best team in the world at the time.
KTB placed third again at PANDORA.TV Champions Winter 2013-2014 after losing 3-0 to SKT K in the semifinals but beating NaJin White Shield 3-1 in the third place match. Although the Bullets weren't considered a very strong Korean team at the time, they managed to sweep the IEM Season VIII World Championship, culminating in a 3-0 victory over Fnatic. They came back to Korea to participate in HOT6iX Champions Spring 2014 but they were knocked out of the quarterfinals 3-2 by NJWS. The Bullets bombed in HOT6iX Champions Summer 2014, missing the playoffs for the first time in the team's history. Mafa was released from the team about a month later. Mafa joined Invictus Gaming as a coach in December.
Mafa coached in his first tournament with the team during the 2015 Demacia Cup Spring Season where they managed to make the finals but lost 3-0 to EDward Gaming. IG placed fifth in the 2015 LPL Spring Regular Season but placed third in the 2015 LPL Spring Playoffs after losing 3-0 to EDG in the semifinals but beating Snake eSports 3-1 in the third place match. In the 2015 Demacia Cup Summer Season, IG placed fourth by making it to the semifinals but losing 3-1 to EDG and then 3-2 to Snake. IG placed third in the 2015 LPL Summer Regular Season and managed to play third in the 2015 LPL Summer Playoffs by losing 3-2 to the Qiao Gu Reapers but beating EDG 3-1. IG qualified for the 2015 Season China Regional Finals and placed second by beating Qiao Gu 3-0 to take the third and final Chinese seed for the 2015 Season World Championship. IG was placed in a group alongside Cloud9, Fnatic, and AHQ e-Sports Club. Unfortunately, they ended with a 2-4 record and were knocked out of the tournament in last place.