This, level 6, is the highest level you can get to legitimately. The location to get the last EXP that will actually count is where you upgrade your Morning Star. Enemies at night are twice as strong but give you three times the EXP. Each level requires you 50 more EXP, starting at 100 for first level up, 150 at second level up, etc. Interesting, as far as Castlevania Two goes.