So with Hunico taking over the Sin Cara gimmick, let's look at the Mistico/Hunico/Sin Cara lineage..
Hunico, aka Incognito, was the original Mistico. He was replaced by the second Mistico, who made the gimmick famous and was the top draw in the world and later became the original Sin Cara. When the original Sin Cara got injured, Hunico, the original Mistico, took over for the second Mistico as the second Sin Cara. Then the original Sin Cara, the second Mistico, came back and the second Sin Cara went back to being Hunico after losing a mask vs mask match against the original Sin Cara. Now the original Sin Cara is gone, and has been replaced by the second Sin Cara, Hunico. So the original Sin Cara once replaced the original Mistico, and now the second Sin Cara, the original Mistico, has replaced the original Sin Cara, who was the second Mistico. So they have each replaced each other once. There is also now a third Mistico in Mexico, the former Dragon Lee.
So...
Mistico became Incognito who became Hunico who became Sin Cara II who went back to being Hunico who is now Sin Cara again.
Mistico II (which was the most famous Mistico) became Sin Cara, was briefly replaced by Sin Cara II (see above), came back, and has now been replaced, again, by the guy above.
Dragon Lee became Mistico III.
Got all that?