Rey Mysterio & Sin Cara are a tag team that debuted in WWE on September 7, 2012. Their team is a Student (Sin Cara) and Teacher (Mysterio) partnership.
Mysterio (a former IC champ) was feuding with The Miz over the Incontinental Title. Cody (also a former IC champ) was feuding with Sin Cara regarding his mask, echoes of his identical feud with Rey Mysterio over his own mask, related to when Cody was injured and had to wear a mask himself.
On the Sept 7 episode of Smackdown, Josh Matthews referred to the pair of luchadors as an "Exciting Tandem" when the pair teamed up and defeated Cody and Miz. Cody and Miz quickly broke apart as Cody, along with Cara and Mysterio, unsuccessfully tried to win the IC title from Miz at Night of Champions 2012 on September 16. Cara and Mysterio were not a team, as it was a fatal 4-way, during that event.
On the Oct 1 Raw, they defeated Primo & Epico in the Tag Team Tournament. This is when they debuted new ring gear. While Mysterio's mask still exposes his mouth and Sin Cara's does not, their masks were otherwise half and half of Mysterio's rounded mask and Sin Cara's pointy mask.