Probably sym, hanzo and hog challenges. in theory Bastion Brick was supposed to be in this Remix, but probably part of the license of the skin is also from LEGO, and without his permission perhaps there is no possibility to propose it again. The same goes for Mercy Pink from the BCRF. and it was not a skin challenge, nor free, let’s stop with this theory: we have already confirmed that Pink Mercy will not be back (see Andy’s blue posts):
on the legendary skins I understood that they choose at random (I do not know that Reaper Raven is famous). they just pick the ones they like recolored. maybe not the same previous heroes, so I would exclude the legendary heroes that came out in the first two remixes.