Fortress is a young kid (I think – hell, I don’t actually know, he looks young) who is strong as proverbial shit.
While this is an old video, he offers a good human flag gem. His main progression was jumping into a tucked position with feet up in the air (min 4:30 in the video). Personally I keep trying to go straight for the flag and I forget to work this progression. Thanks for the reminder Fortress.