The custom here is the flying horse, Valinor. The Black Knight shown is the stock figure with a replacement sword. Valinor was made from Aksh, the horse in the Prince of Persia line, with the wings of "Toothless" from the How to Train Your Dragon line. (Black Knight has also flown with a white winged pegasus named "Aragorn" - which he bequeathed to Valkyrie at some point - and an "atomic steed" flying cycle that he used primarily in his 90's Avengers stint.)