Update 09/10/2012: It seems from forum postings around that this is not out in our english iOS version of the game yet.
The title does sound like some health product but no, this is supposedly a Guardian in the game. I posting the main part of the guide to get it here as I have encountered a case whereby I linked something but the webpage was gone.
From garisonmp3z in Rage of Bahamut Forum post:
"-Have completed all the main and subquests.
-Have all the 1-3* star cards in your catalog.
-Have attained at least an A+ rank in Coliseum.
-Have all the special hunter cards from the volcano hunting ground big monsters such as Genbu.
When all these requirements are met you must go into the first hunting field with 1 slot left in your card inventory. ROYAL JELLY will not appear If this requirement is not met.
ROYAL JELLY looks like a regular slime model and will not always be awarded. You may receive a silver slime instead or a normal slime.
ROYAL JELLY has the following stats: 1 of each.
It has two uses.
It can be used as a card in battle and will hit your opponents deck for -20% atk/def/wisdom and agility to all their cards at once.
ROYAL JELLY is easily destroyed in 1 hit so be cautious.
OR ROYAL JELLY can be used to add 300+ stats to any card for a onetime use only.
After being used ROYAL JELLY will be gone. You can always go hunting for more ROYAL JELLY. However a card enhanced with ROYAL JELLY cannot be enhanced again with it. ALso, only 1 ROYAL JELLY may be used in battle at any time."
