Zelda II: The Adventure of Link/Barba
From Red Candle
Zelda II runner Carapace has put together a Guide to Jackhammer Barba, explaining just how to use the downward thrust attack to take care of the Palace 6 boss quickly.
The details may be different for the Japanese version, as Barba/Volvagia is taller there, but the principles are the same (and you even get a ledge on the left in the FDS Zelda II).