Discovered by Fluffy Kitten
In hyrule castle you normally need to talk to Malon to get an egg, then wait for it to hatch and use the chicken to wake up Talon. To skip this, first you need early bombchus from the Spirit Temple. With the chus go to hyrule castle, forget about Malon and Talon. Go to the area with the boxes and right above the moat will be 3 steps. Get on the highest step and face the wall up where the crawlspace is. Hold Z and take out a chu, run off the edge, quickly press R then B. The damage boosted jumpslash should be enough to make it to the ledge, if not then your timing may be off a bit (the shield drop and jumpslash must be done as soon as you jump off). This also works with bombs if you decide to get those before lullaby.