Stage Select / 100 Lives
Booting Vampire Killer in conjunction with Konami's "Game Master" cartridge allows you to select both your starting level, and quantity of lives from the title screen.
Freeze All Enemies
Before fighting the first boss, have the Hour Glass equipped, and after defeating it, use the Hour Glass just before the level end theme finishes. If done correctly, you will start the next stage with all the enemies permanently frozen for easy kills.
You can progress until the last level, but to undo the glitch (a must before fighting Dracula), simply use the Hour Glass again.