Isshin may be my favorite boss to fight in all of FromSoft and he’s awesome. But I’d give Demon of Hatred the most difficult boss in the game title. And if we’re including subbosses the 7 Spears and general wrecked me. So sad there was no dlc for Sekiro.

Anyway, most difficult final bosses I remember getting repeatedly killed by Tabuu in SSBB. Don’t know if that holds up, since I haven’t played brawl in a long time.