The approach to the Throne Room is a gauntlet of the toughest enemies in the game. Expect to encounter multiple Knights, Axe Armors, Bone Golems, and Flea Men. There are often spike traps and crushing ceilings. Conserve your health and hearts as much as possible. This is where your chosen ally can make a huge difference. Sypha's screen-clearing spells, Grant's mobility, or Alucard's bat form can help you navigate these final challenges.
Make sure you have a good sub-weapon equipped and a decent supply of hearts before entering the final boss chamber. The Cross or Holy Water are generally excellent choices for the upcoming battles. If you have Sypha, ensure she has enough hearts for her powerful spells. This final stretch is designed to drain your resources, so play cautiously and strategically.