Contains Spoilers!

Giant Bat
The Giant Bat is no new boss to the series and just like the other Giant Bat bosses, this one fights pretty much the same.  His main attack is just hovering around and stopping occasionally to spit out a fireball and even this is done slow enough to give you time to attack or stop the attack.  You can only hit him three times before he breaks up into bats and flies away.  His secondary attack is to drill into the ground.  If anything you want him to do this because while he does you can hit him about four or five times.  Beating him doesn't really give you much, unless you fought absolutely no enemies at all in the level you probably won't even level up from him.

Living Armor
Living Armor can only do two things.  Walk forward and backward, and swing his sword.  All you have to do is hit him a few times and either way he will walk, but when he stops it means he's going to attack.  Just dash in the opposite direction and you avoid that very weak and only attack.  Just keep pushing him away from you and you'll kill him, that's pretty much it.  After killing him you get the Lizard's Tail which allows you to slide.

Skull Knight
The Skull Knight is a boss from Castlevania III: Dracula's Curse.  This time he has three "forms."  They don't look different, just different attack patterns.  His first form of attack is he has his shield and sword.  If you see him lunge back for a second you should dash away from him because he's going to stab at you and does have a long reach.  After hitting him enough times he'll lose his shield and disappear.  When he comes back up he'll still have his shield but no sword.  Now all he'll do is either jump or walk around.  When you see him put his shoulder out and start flashing jump on a platform, when he disappears jump in the direction he came from to avoid getting hit by him or his horns.  After enough of this he again loses his shield and disappears.  His third form of attack is he has no shield.  He again either walks or jumps.  His attack is to shoot a laser beam out of his chest.   The Good thing about this is that you can safely stay near him and duck and whip.  You can kill him very fast doing this.  In fact I recommend ducking the whole time.  If he jumps towards you just slide underneath him then get close again so you can attack while he shoots out the laser.  Killing him gets you the Sylph's Feather.

Golem is another easy boss.  His main attack is to jump which causes rocks to fall from the air or two do a slow punch that can be avoided by dashing backwards.  If you really want to do damage to him real fast use crosses from a distance so they'll hover over him for a second or two and do a ton of damage.  After getting hit enough the rocks fall away from his face, now you can only hurt him by hitting the red ball for his head that looks a lot like the Bloodlines Golem.  His attack now is to after a few steps spit a bunch of rocks out.  You don't want to be near the wall when he does this if he's close to you.  The best way to do damage is to just throw crosses at his head when he does this, and when he walks just whip him.

The Minotaur still attacks the same way he has since Dracula X, only this time he's even easier and attacks slower.  What you want to do is go close to him and throw as many crosses as you can.  This causes him to jump back, and you need the room.  When he has his axe above his head you want to dash back two or three times because his attack takes a lot of space.  His other attack is to duck and charge at the wall, just jump over him.  When he's stuck in the wall throw one or two crosses at him for more damage and then dash away because when he jumps out he'll land near the middle of the room.  Keep repeating and he'll die pretty fast because of the crosses.

Devil is one of the more annoying bosses.  He isn't particularly difficult, the fight can just be annoying.  If you touch him you'll get cursed, so you have to be careful to not touch him by jumping into him or anything.  I think it's easier to just whip him in the air and then throw crosses at him when he's on the ground.  His main attack is shooting fire at the ground which is easy by just going behind him.  When he goes on the ground he'll shoot fire towards you, just duck under it.  At this time is when I usually throw crosses.  If you're too close to him when he's on the ground he will also punch at you, again be careful to not get hit or else you'll be cursed.

Giant Merman
The giant Merman pretty much just rolls on the ground at you for an attack or will call other Mermen to attack you.  To avoid his roll just jump over it.  And when he calls other Mermen you can kill them pretty fast yet the boss will still stay still and tell the now dead Mermen to attack.  Using this to your advantage you can throw crosses on him and whip him to help speed up his death.

Max Slimer
Max Slimer is the second boss in a row of very easy and lame bosses.  He really has no attack, it just moves across the ground.  Just whip him and throw crosses to end the fight quicker.  As you do more damage more pieces fly off former smaller blobs of slime, just kill them.  Sometimes he'll go and stick to the ceiling but then later come down.  That's pretty much all there is to this boss.

Peeping Big
After you hit the eye once it's tail will come out, this boss might be easier if whipping it didn't make the boss nearly freeze.  It's main attack is to have it's tail whip around in a circle, and it's only once, and the thing can't move while it does it, avoiding this is a joke.  It's secondary attack is to close its eye and pull it's tail in then hop across the room.  You can either double jump over it or slide under it, or just let it hit you since this thing barely does any damage, and unless you jump into the boss or something you probably won't get hit anyway during the fight.

Legion (Saint)
The Legion is pretty easy, but unfortunately it doesn't drop little corpses that come to life on you.  When it is covered in bodies it will just fly around the room with an eye floating out of it every now and then to run into you.  If the eye hits you you'll be cursed.  To hurt the Legion you just need to expose some of the core, and the fastest way to expose the core is to throw crosses at it.  Because of it's very large size this does enormous amounts of damage and you can very quickly have three fourths of the core exposed.  If the core is exposed at all you can still do damage to it.  Once all of it's covering is gone the core will grow three tentacles.  These tentacles just move around randomly pretty much.  Every now and then the tentacles will go up and shoot an energy beam from it.  Usually it doesn't even look like it's aiming for you and just doing it for no reason at all.  It's pretty easy to avoid, but if you do get hit by it you should be a little more careful because the beam does a lot of damage.  The best way to attack it when just the core is exposed is to just whip it and throw crosses when you know you can get it to hover over it.

Shadow is just a shape shifting boss with weak attacks and possibly the stupidest transformations ever.  It's main form is a face but it can't be hurt in this form.  Next he'll turn into a panther.  This just charges from side to side of the room, and the last thing it will do is making a howling animation, when it does this it means it's going to jump over to the center of the room and revert back to its face.  When it's in a panther form just hit it as it runs by you and have a cross over it when it does the howling motion, you can get a a few good hits in that way.  Eventually it will go into it's next form, a flying pirate cutlass.  This one just hovers around the room like most of its forms.  It might try and home in on you once, but it's still slow, and it doesn't directly home in on you, it just goes near you.  You can whip it when you can get a safe hit in.  If it touches you you'll just get cursed.  You can use crosses on it if you can get a good chain of hits, but otherwise I wouldn't worry about it.  After this it again goes into it's face mode, hovers around, then goes into it's last form, a big moth.  This at least does something, it will fly around the room dropping spores on you that can poison you, and that's it.  Whip it and throw crosses.  That's all there is to this entire boss fight.

Pazuzu is a a little more difficult than all the other bosses thankfully.  Pretty much all he does is jump if you think about it.  His main attack is to spit out fireballs, at the start of the fight it will be just one.  Later on though he'll be spitting out three waves in a row.  The time to attack is when he is standing around or doing his secondary attack.  His secondary attack is to get a bunch of imps to come in the room and attack you.  When he does this throw crosses and whip as much as you can, because this is when he literally does stand there so he will take a lot of damage.  He's still an easy boss, but not as easy as most of them.  Killing him unlocks a good chunk of the castle. 

This Minotaur is a bit harder than the last one and will actually do some damage.  Basically instead of an axe attack it just throws the ball at you, it still takes a lot of space.  I think that the ball attack is a bit harder to get away from through because if you're close to the wall you can't do anything with axe attacks you could at least do something.  Anyway to get yourself as much room as you need you want to go near his legs and use crosses, this still makes him jump away.  Pretty much that's all there is to do.  You could do a spell fusion with the cross and fire spellbook, that would most likely do some nice damage too if you had the Minotaur cornered.

Legion Corpse
Legion Corpse isn't any harder than the original Legion.  Instead of breaking away to the core you have to hit the outer shell to expose its weak point.  It's weak point is the skeleton the comes up from time to time.  To get it out just hit the shell continuously, if you stop it will recede back.  The fastest way to bring the skeleton up is to use crosses, that's really the only way to get a nice number of hits very fast.  When the skeleton comes up just whip or use a cross on it, the boss is easy enough.  Legion Corpse only has one attack and that is to have small things fall out of it and crawl at you.  You'll either be cursed or poisoned if one touches you, but that's about it.

Talos is the big knight who originally chased you at the start of the game, now is your chance to fight him.  His only attacks are to grab at you or he'll replace his hand with a blade for an attack.   I'd say your more likely to get him by him walking into you than him actually connecting with an attack.  Everything can be avoided by just dashing back and he is slow, so you'll be able to know when to dash back in time.  The only way to hurt him is to hit the glowing red spot on his leg, it's whip height so you don't need to duck or jump to get at it.  You do want to keep him as far away from a wall as possible, because if you don't have enough space to avoid his attack you will get hit, and his attacks do a pretty amount of damage.  The best way to keep him back is just whip at his leg, you can throw crosses but in this case they don't do very good damage.  Since he is almost constantly moving it's hard to get the cross over him.  You can still use it if you want.

Finally you get to fight Death.  His attacks are just the same as in all the other Castlevania games.  He has a bunch of small scythes flying at you, and he teleports behind you to try and hit you, also he'll sometimes throw his scythe at you to try and hit you.  Try to avoid getting hit by any of his direct attacks, they take off a lot of hit points.  When he's hovering around just whip him or throw crosses.  He does hover in one spot a lot, so those crosses add up.  If you're about to get hit by some of his attacks and want to avoid it just do a spell fusion technique.  After doing enough damage Death goes to his second form.  The second form of his just crawls around the top and bottom of the screen.  The best way is to just avoid getting hit and take it slow.  To hurt him just hit him in the head.  You can safely jump into his rib cage area when he's on top of the screen so then is when you can whip him a lot or throw crosses if you want.  The only area to avoid is his front scythe arms, his head, or touching his tail.

Cyclops is a fine boss to have for the Heretic's Grave area since the level is basically a remake of the cemetery from Castlevania III.  Anyway, unlike in Castlevania III the Cyclops finally uses his hammer, which also happens to be his main attack.  Is secondary attack is his charge.  He is moderately quick, so you can get hit pretty easy, and since there isn't much recovery time those hits can and will add up.  Through out most of the fight though he will just either be walking or standing still, that's your best time to attack.  The whip should be fine for now, you could use crosses or holy water.  By now you have all the spellbooks hopefully, so you can do what you want.  The cross summon is pretty strong.  It's pretty much up to you on how you want to fight bosses at this point.

Evil Maxim
How fitting that the last two bosses are the only ones where I nearly have a spell fusion attack as a requirement.  Maxim can just be that annoying.  I highly recommend wind+crosses, that barrier will save you from so much.  Maxim has quite a few attacks.  He'll attack with his sword, one attack will usually hit you once due to the low recovery time.  He has a cross shuriken which is best to just double jump over, he can make a double of himself, really not good, and his super attack, making a bunch of clones fly out of him at you.  Make sure you have a lot of potions and items to restore your MP.  Always have the cross barrier out, it protects you from his super attack, it does a lot of damage, and sometimes it stuns him.  When he's stunned you can whip as much as you want.  I suggest just running away from him with the cross barrier, it saves your health, attacks him, and is better than getting hit because of bad recovery times.

Dracula's first form is nothing you have not fought before if you've played past Castlevanias.  He teleports around, throws out three fireballs, his other attack is to shoot out the giant fireballs from Dracula X, only instead of just two he shoots out about six.  I recommend just throwing crosses at his head, but that's just me since I've been doing that since the original.  Eventually he goes to his second form which consists of all the pieces you collected during the game.  It only has two attacks, shoot a very powerful laser beam from its eye, which can be avoided by just ducking, and it's second is to attack with it's claw.  This is again where I would turn on the cross barrier, it can do a lot of damage and attacks for when he does the eye laser.  If he tries to get you with the claw just jump away or slide.  Most of the time the thing just floats, but you need to still watch your health, if you get hit you will take a lot of damage.  If you don't want to use spellbooks then crosses would do a ton of damage, and you can get in whip length to attack with the whip when he does laser attacks.