We could potentially make a whole thread out of this... We'll see.
Anyway, did you know in CV3 that if you turn Alucard into a bat and fly along the water in the sunken ruins, Al will make the water splash and he'll bounce upward off the water.
Rubble from smashing blocks counts as one of your attacks.
Sypha's ice magic can kill White Dragons in two hits (freeze then smack with staff).
Sypha's Ice Magic has no effect on the Bone Dragon King.
Sypha's staff rapes the Bone Dragon King.
Fleamen/Gremlins leap at you when they are near and you face them. After five leaps, they run away.
Slimes leap at you when you look away from them then jump off the screen and fall down on top of you (like in "The Blob"). Sure, ya knew that; but did you also know they can jump into a wall and fall to their deaths if you're Grant? Bet ya didn't know that!
Crows will swoop down at you eight times and then retreat straight across the screen in your direction.
You can duck under Dracula's spit in his second form in Japanese CV3. (Yeah, you probably knew that by now).
Death's skull form will reflect the Cross back prematurely, although if you throw the cross the opposite direction first, it will hurt him.
There is boss data missing between The Creature and Death -- someone was removed from the lineup. (You'd know this if you've been around a few months.)
Medusa has two sound effects in CV3, neither of which work.
You can't freeze the dripping water in the catacombs (go figure).
Boss Alucard's flames can be frozen by Sypha's Ice but will still hurt you if touched.
The Giant Bat boss can only fly so low, so you can in essence duck under it until it passes, although this is a time waster.
You can't fall off the far right side of the section in the mountains where rocks just keep falling and falling on you, but Grant can climb down it to his death; if he stops partway down, he'll be stuck in the wall. You can then wait until the blocks have filled up the screen then crawl up the wall (you can't jump because you're stuck in the wall, but you can still crawl). Getting across the chasm from that wall to the stairs is a whole other issue.