Heres the rules, courtesy of Irish Poker Boards;
Mythical is a variation on Gin Rummy played with 2 full decks of cards and without jokers.
Players: Recommended Max is 4, minimum 2
The deck is thoroughly shuffled but never spread out face down on the table and each player cuts the deck, the lowest exposed card gaining the deal.
Each player is then dealt 10 cards face down with the deal going clockwise.
It is the dealer's responsibilty to ensure all players have no more than 10 cards, if any player has more than ten and the first card is turned over he must finish his hand with that number of cards. If he has less he must "dip" (see below) and not throw on his first turn. A player with 11 or more cards CANNOT finish with 4 sets or 3 quads. He must have at least one Straight Flush. A player with 11 or more cards is still entitled to use a Mythical Card.
The dealer then places the top card of the deck face up on the table and the game begins.
Object: Players must attempt to make 3-of-a-kind, 4-of-a-kind and straight flushes (3-card min, 5 card max although obviously a 6-card sf would be split into 2 threes). A player is deemed to be "out" when he has no cards in his hand which do not fit into either a straight flush, a set or 4-of-a-kind.
The MYTHICAL Card: A "Mythical" card may be used to finish a players hand. If, for example, a player has 3 queens, 6,7,8,9,10 of hearts and 2 kings he may designate his Mythical card to be a King. This is an IMAGINARY card which is used as an eleventh card. All cards in the hand must be used in order to finish, whether with or without a Mythical Card.
Playing order: Players take it in turns going clockwise from the dealer to either take the top card off the deck or take the top card from the face up pile which is begun when the dealer exposes the first card.
Note: Taking from the deck is known as "dipping"
After a player has taken a card he must dispose of one card from his hand, or alternatively throw the card he has just taken. THROWING THE CARD SIGNALS THE END OF THE TURN. If a player throws and then declares himself to be out he must wait one rotation before the game ends.
Getting "Out": Once a player has completed his hand he declares himself to be out and lays his cards down on the table in sets, quads and straight flushes. He then, AND ONLY THEN, discards his final card.
Each other player must then place his cards on the table in sets, quads and straight flushes and the point total of each players remaining cards is used to determine the score.
NOTE: Each player, whether they are out or not, is allowed one, AND ONLY ONE, Mythical Card to use in their hand. This can be used when putting hands down to determine points to reduce points totals.
Calculating Points: The face value of each card is the equivalent value for points. Picture cards are all worth ten, as are aces. HOWEVER, Aces can only be used as low cards in your hand. Hence Q-K-A is NOT a Straight Flush while A-2-3 is.
Players designate prior to the game how much a point is worth. The most common structures are as follows:
50c Per Point, 1euro for the game, 2 euro for the Mythical
50c Per Point, 2euro for the game, 5 euro for the Mythical
1euro Per Point, 5 euro for the game, 10 euro for the Mythical
Therefore if a player has 15 remaining points in his hand he pays either 50c per point or whatever has been settled on.
If the player who is out has used a Mythical Card he does not receive the Mythical bonus, however if he does not use a Mythical Card he does. A PLAYER CANNOT RECEIVE BOTH A GAME AND MYTHICAL BONUS. A player indicates if he has not used a Mythical Card by declaring "bonus" when putting his hand down.
Any player, at any time, can call for a mix. This is where all players discard their hands and begin a new hand. In 3 or four way games the player who first asks for it must place the value of the Mythical Bonus into the pot while all others place the game value into the pot (i.e in a 50c/1euro/2euro game the player who asks for it puts in 2 while all others put in 1) This is called the "Mixing Pot" and is awarded to the winner of the next hand. There is never a mixing pot heads up.
Calling "Out" Incorrectly
If a player calls himself out and places his cards on the table but is, in fact, not out, he must then leave his cards on the table and may only take face down cards from the deck and not from the discard pile until he is out or someone else is. He may NOT change his hand around on the table. For example if he has 3h,3c,3s; 4h,4c,4s; 5h,5c,5s arranged as sets and has a loose King in his hand and dips the 6h the player may not re-arrange his hand into 3 straight flushes.
Hope its of interest.