Castlevania/Secrets

Bonuses
Throughout the castle, there are several special bonuses including money bags (1000 points) and crowns/treasures (2000 points). These nearly impossible to find bonuses are revealed by crouching or standing on appropriate blocks.

The second quest has a few more secrets which can be seen in this video:. Moai figures (4000 points), a reference to Konami's Gradius series, can only be found in the second quest.

Pot Roasts
Life restoring Pot Roasts can be found by destroying certain blocks throughout the castle. Each Roast restores six bars of health, so finding one can easily be the difference between life and death.

There is one additional Pot Roast exclusive to the second quest.

Shot Multipliers
Shot Multipliers allow you to have two or three special weapons on screen at once, which lets you kill things, especially the bosses, much more quickly. Multipliers can be dropped by enemies or candles, but also found in certain blocks.

There are a couple Shot Multipliers exclusive to the second quest.

Miscellaneous
There are a couple smaller items hidden in blocks.

In Stage 13 and 15, there are some hard-to-reach candles. These can only be hit by the Throwing Axe, which would need to be brought in from a previous stage. These candles only contain Small Hearts.

Second Quest
After you beat Dracula and the game one time, you can continue after the credits roll. You will begin back at Stage 1 with any special weapon that you had the last time, but the game will be much more difficult. Every time that you get hit, you will sustain four units of damage, so you can only be hit four times before dying. The enemies also come in larger numbers and move significantly faster, though they don't take any additional hits to kill.

The stage counter does not reset when you begin the second quest. You start on Stage 19 and the stages progress in the same order as the first quest, though there is a small difference in their numbering. Stage 19 is the area outside of the castle and Stage 20 is the interior. In the first quest, both of these areas together were Stage 1.

After defeating Dracula a second time, the second quest restarts and the difficulty does not increase further. The game loops forever this way. At Stage 99, the stage counter will stop incrementing, but the game will continue normally.

Additional changes:
 * Stages 1 - 3: In all above grounds sections, Bats will be constantly flying about, often at the most inconvenient height possible. Fishmen and Ghouls will also appear in much greater numbers.
 * Stages 4 - 6: All three stages are now populated with Medusa Heads. The spikes in Stage 6 now pose one of the greatest challenges of the game since you also have to time your movements to avoid the Heads.
 * Stages 10 - 11: Many, many more Bats than before, who now appear alongside the Eagle/Fleaman teams (which also appear in greater numbers). The Fishmen are much more numerous in the underground river and may jump up directly below you.