For me, it is absolutely impossible to survive as soon as the BFB appears. The foot will always land directly on me, instantly killing me. Due to this, I never made it past day 24. My only hope is to avoid the shadow at all costs, but if I ever by accident touch the shadow, its an instant game over for me. Absolutely unavoidable. I am severely frustrated because of this because I lost several worlds now because of this and I can't for my life make any progress.
wait until BFB spawns, try to surive for as long as possible, eventually step into the shadow and immediately get killed.