Know Thy Enemy

Watching a longplay video of Vampire Killer on the MSX2, I noticed minor differences between enemies in VK and enemies in CV1. It was clear the enemy behaviors and code were under the same direction for the most part - most enemies behave nearly identically except for a couple minor differences (I'm leaning toward stripped code for the sake of saving memory). I'm not a fan of CV2's enemies - they seem too overly simplified and dumbed down. In CV3, you can see the similarities to the old enemies in CV1.

My point is, even though enemies may seem nearly identical between games, there are some significant differences between them all. The biggest difference is timing. Collision checking is also another issue (CV3 was much more meticulous in that area). Those are minor things most gamers wouldn't even notice, though. However, the behavior codes themselves do vary between games.

Bats
In CV1, there are two flying bats. The ones at the beginning of the game are nearly identical to those in CV3, but those in the underground river have their base wavelength quadrupled. If Belmont is in the middle of the screen when a bat appears, all he has to do is stand still. In CV3, there is only one flying bat - the size of the wave is based on initial vertical and horizontal speeds.

Fleamen
In CV1 (and I think VK), they will chase Belmont forever until something injures him, at which point they'll just continue hopping forward. When Belmont's invincibility wears off, if fleamen are still on the screen, they'll resume chasing Belmont. In CV3, they'll hop forever until they've made 8 leaps (the high jumps), at which point they'll hop away from Belmont off-screen.


Crows
Huge difference here. In CV1, crows swoop toward Belmont then fly straight toward him. If the conditions are met, they'll fly backwards straight off-screen. I just discovered this was in fact a bug in the code due to the programmer calling the wrong subroutine in state 3 of the crow's code. In CV3, they will swoop 8 times before flying straight off-screen.

Ghosts
In CV1, ghosts appear out of thin air. In CV3, ghosts flicker into existence. Also, the timing of their direction changes is different.
  
Skeletons
CV1 only had Bone Skeletons and Blood Skeletons. Bone Skeleton conditions were a little more lax than in CV3, so getting a double bone toss was pretty common. Blood Skeletons hobbled along. In CV3, Blood Skeletons came with or without a whip and both forms were identical to their non-blood counterparts; there was no hobbling skeletons in CV3.

Bone Dragon
The difference between CV1 and CV3 is notorious and doesn't need to be documented here. CV1's code was just plain bad.