How to Get Infinite Lives
Alright so to start off, I'm not 100% certain what the upper limit is but I got my extra lives counter to 11 so it does go above 10 and assumed up to 99 at least.
The first thing to understand is that the graves that drop the armor will drop extra lives when you're carrying an extra armor on the top of the screen.
The second thing is that the game checkpoints after every couple screens, so getting killed before entering the forest will put you back at the start screen.
The third and last part is that falling in a pit (such as the one on the screen before the forest), does not get rid of the armor you're carrying. This all adds up to if you can clear the first two screens with enemies without taking damage, break both armor gravestones, and then jump in the pit before the forest, you'll get +1 extra lives each time you pull this off. The frogs are pretty easy to time and kill without taking damage, the ghost however does take a bit to get used to jumping over with the old school Castlevania jump arc.