I've been replaying the USA Castlevania III: Dracula's Curse on my NES and TV, and I've been noticing some interesting things I thought I'd share:
1. Grant can crouch under the Bone Pillar's upper fireballs, a Gates-of-Death's chainwhip strike, and a Dhuron's Sword Thrust.
2. Grant can jump over the Cyclops's Dash Attack.
3. Grant can destroy Medusa on the Haunted Ship by chucking Axes from the ceiling.
4. Alucard's Bat-Transformation can be used to safely pass through the Cyclops's Dash Attack, if timed just right, by transforming right as you're about to jump into his eye.
5. The Orphic Vipers on the Moat Bridge seem to take excessive damage from Sypha's Lightning Bolts spell.
6. Doppelganger is difficult, but if you have Grant you can crouch-stab him to death if you're lucky enough. The Doppelganger will spend time chucking Axes at Grant, which sail over his head, and rarely throws the Daggers. Not sure whether one can crouch under the daggers, since Doppelganger was stabbed to bits way before he could launch one.
7. Sypha's Lightning Bolts fail on Death's 2nd Form (mostly), since they have issues tracking the giant skull. They also erroneously attempt to attack Dracula's Third Form's floating platforms. I guess the Bolts think the platforms are enemies.
8. If you choose not to go to the ClockTower at the beginning, you instead go to the beginning of the Forest. This stage is the only one that's a 0 stage; most stages are 1-01 or 4-0A, while this one is 3-00.
9. Although after you talk to Grant you're climbing back down the ClockTower, the stage numbers actually continue to increase. Meaning 2-01 and 2-06 are copies of the same level. However, some item placements different between the 'going up' and the 'going down' versions of the otherwise identical stages (there's an Axe midway through 2-02 that isn't available in the same candle on 2-05, and there's an extra candle at the end of 2-06 with a big heart, that isn't in the going up version 2-01).
10. Crumbling blocks won't crumble if Grant is clinging to them from their underside.