This item is a staple of Dark Castle, found in each game in the series, and acting as a major gameplay element. In Dark Castle, Dark Castle Mobile and Color Dark Castle, when you are touched by a rat, or bat when carrying no elixirs, you die. This was later changed In Beyond Dark Castle, and Return to Dark Castle, as a health system was included. The elixirs were made by The Wizard.
In the original Dark Castle, it didn't tell you how many elixirs you where carrying in a number, but instead had an icon for each one you where carrying up to 6. You could carry as many as you collected beyond that though.
In Beyond Dark Castle they did away with the icon system, and showed how many you were carrying with a number. You can carry 50 Elixirs max in this game.
Dark Castle Mobile used the same system as Beyond Dark Castle.
Return to Dark Castle Also uses the same system, although you can now carry up to 99 Elixirs.
The appearance was reverted back to a bottle in Return to Dark Castle, though it kept the colors from Color Dark Castle