An aquatic-themed level. You'll face more Axe Knights, as well as the Fishmen from the water.
Hunchbacks await you at the start. You can merely wait, and they'll come to you, so you can easily get rid of them. Up the stairs is an Axe Knight. There are no platforms to help you, so you'll have to face it directly. More Hunchbacks after the stairs. The candle on the left, right below the right stairs, contains basic subweapons. This means a useless Knife for Trevor, but Sypha may benefit from the Fire Book if you aren't bringing over any subweapons from the previous stage. Take the door.
In here, you'll notice a stream of water over the blocks. The stream pushes you left or right, depending on which side you're on (which is split by a waterfall in the middle). Don't worry if you fall into the leftmost alcove where the stream leads into a waterfall; you can't fall to your doom here even if you duck. Fishmen periodically swim near you in the water, indicated by a dark shadow moving in the stream. They'll then stand up and shoot a fireball. You can kill them quickly when they stand before they shoot, or even before that while they're in their shadow form. If they do release their attack, however, the best option is to just duck under the fireball if you're in the water with the Fishmen. Ravens try to swoop at you in tandem with the Fishmen's attacks, so try to get rid of them before they become a nuisance.
The third candle holds useful Holy Water for Trevor, but Sypha gets the Ice Book, which has in interesting effect in this stage. While on this stream, you can use the ice to momentarily freeze it, also trapping the Fishmen while the water's frozen. In this state, you can walk on top of the frozen water, heedless of the pushing effect the normal water had on you. You can use this to your advantage to make traversing to the right easier. Also, the waterfall in the middle won't impede you if it's frozen, so if you choose this option don't worry about that. Make sure to hop the gap at the right end, and if the water's frozen, it's best not to stand over the waterfall as it's likely it'll thaw too soon and you'll fall to your death.
A Bone Pillar guards the door right. Make sure its fireballs don't send you off the left ledge into the pit. The part below the door can only be gotten to with Alucard or Grant. Take care of the Bone Pillar, then go through.
Go right, and you'll have to contend with a Hunchback and Axe Knight. If you go far enough to spawn the Hunchback, it'd be best to return left a bit and kill it before taking on the Axe Knight. If you got the Ice Book for Sypha earlier, that'll make dealing with both enemies easier. The upper platform contains a Big Heart. You can get it with Grant or Alucard, and Sypha can get it as well by freezing the Bone Pillar after the pit and jumping atop it, just make sure to do so before it unfreezes. Head downstairs now.
Look out when you go down, because a bat will come from the left or right side. It has a higher chance of hitting you from the left if you're slow, but if you simply keep walking down to the platform you'll be fine. Another out of reach heart can be reached with Grant, Alucard, or Sypha. The bats in here continue to come from either side every so often, so you can stand on the upper left platform and freeze one when it's in range if you want to get it with Sypha.
As you make your way right, be cautious when passing over the platform comprised of two bricks and stairs on both sides. An Axe Knight awaits you on the next platform. If you jump here, you're more at risk of getting hit by a sudden axe or fireball from the above Bone Pillar, so it's best to just walk down the right stairs and deal with the enemies then. Head up.
Going up the stairs, another Axe Knight will try to defend the upper platform. Wait for an opening before proceeding. The candle up here contains a Stopwatch. It might help in the upcoming area, but watch your heart consumption if you decide to use it.
Before going through the right door, the block above it contains meat if you need health.
Kill the Raven immediately, because you don't want it following you here. The second candle holds a basic subweapon, so you may want to forego it unless you don't have one. Once you jump the pit to the next platform, do not stop moving right. The platforms will collapse, and it'll be nigh impossible to not fall if you're too slow. Beware of the Ravens that try to hinder your movement. You can watch for their initial swoop. If they reach their pause phase, you ought to be able to hit them then. If they continue for you, however, make sure to jump and hit them before they touch you. The final two blocks here will not fall, so you're safe if you make it here. The rest of the stage is solid ground as well, so you no longer have to feel hurried.
Fishmen will jump to the platforms near you from below as you make your way right, to the stairs. Watch that one doesn't jump in your path, especially while you're jumping. If any are in an inconvenient spot and you have trouble getting to them, just wait because they'll jump back down eventually. Don't dawdle before the stairs platform though, because they may keep popping up near the stairs making it hard for you to jump down. Also, make sure you actually jump to that platform. Head downstairs.
From here it's a straight shot to the boss: Water Serpents. The third candle holds an Axe for Trevor, and the Fire Book for Sypha. If you're still carrying Ice from earlier and you want to use Sypha for the boss, be sure to pick up the Fire because Ice will not work.
Defeat the boss, get the Crystal, and you'll get to the next part: Stage 7A: Castle Courtyard.