Breather Level: On the Alucard path, opting to finish Stage 5 rather than going to the Sunken Ruins takes you to the Catacombs beneath the castle. It's unusually short, has fairly simple challenges, and both Grant and Alucard have ways to make it even shorter. Even the boss (Frankie, who also appears in Stage 5 of Sypha's route) is pretty easy.
The Castle Entrance is this on all paths, despite the fact that from this point on you die in four hits. It's short, light on the bottomless pits and tricky jumps, and allows opportunities to get lots of hearts. The boss is certainly not that easy though, considering it's Death.
Ensemble Darkhorse: Alucard was a relatively minor character in this game, but he evidently had enough of a fanbase to later become the main character of Symphony of the Night.
Death is this as usual. He flies around summoning scythes and you die in four hits like the encounter in the first game, only he has a second form this time round. Fortunately, the second form is easier than the first form, and the first, while really hard, is not as brutal as in the first game due to you having more options and room to manouver.
That One Level: Stage 7-5. The only way to advance was to wait for the falling blocks to form a platform for you to ascend. If you got hit by a falling block, you were likely dead, and had to repeat the process from the start.
Stage 7 as a whole could count, seeing as it's about as long as 2 normal stages. The best part? The hardest parts are AFTER the falling blocks, so every time you game over, you have to go through them again.
There's also Stage 9, which is almost all the different challenging segments remixed into one big ass stage. The fact that you die in four hits at this point is the icing on the cake.