Anti-Climax Boss: Dracula Wraith in the path to best ending, as it has only two easily avoidable attacks and just stays still as you whack it to oblivion. Considering that the previous fight against Maxim actually requires some degree of skill, this comes off as little pathetic.
If you can get past the NES-like synthesized tones in the music, this game actually has some of the most haunting melodies heard in any of the portable Castlevanias (in particular, the theme heard in the bad ending), and a few badass tracks like the medley "Vampire Killer 2002".
The game lets you hold up to 99 of any item, as opposed to 9 in newer games. With enough money, you can easily buy 99 Potions and Hi-Potions, which makes survival trivial.
Maxim mode itself gives you the use of Maxim. And god, isn't he broken. Multi-hitting Shuriken Sub weapon, Invincible Rolls, FAST Stab attack, EVEN MORE FAST crouching kick (despite its pitiful range though), and a Street Fighter command-esque move that is so powerful it wipes out boss easilly. Sure, it's a Bonus Mode, but try him in Boss Rush, and see how broken he really is.
Cross + Wind Book. It creates a bunch of floating crosses that circle around you for pretty low MP cost. Those crosses won't disappear until they hit a certain number of times. It breaks both mooks (usually nothing will be able to get close to you) AND bosses (crosses hit many times before they disappear, constantly dealing damage).
Goddamned Bats/Bosses: Anything that can curse you, thanks to this game making said effect even more annoying than usual and also using it very frequently.
Nightmare Fuel: Legion, of course, but now in two delicious flavors! The standard Granfaloon "Destroy its outer layer of corpses, then whip the core" Legion and a new, more terrifying "Corpse" form, which involves whipping open a giant wound to attack its weak point — a crucified skeleton! And the sounds it makes! Yay!