There are only three parities and all of them are edge pairing parities: the first one is a case where a single edge is flipped. You fix this with the same algorithm for the single dedge flip on a 4x4x4 which is r2 B2 U2 l U2 r' U2 r U2 F2 r F2 l' B2 r2 Then you have a case where you have to make 2 more thredges but there are nomore unmatched pairs to trade out with, you can then send the piece on the left of the right corner (lolwut? well, the third edge, on the right) to the other side, with the algorithm l' U2 l' U2 F2 l' F2 r U2 r' U2 l2.The third one is just a combination of the two parities I just described, so you only need to know these two algorithms. No OLL/PLL parities happen, so when all of your thredges are solved, you no longer have to worry about encountering a parity error.