Cannot be Normal Summoned/Set. Must be Special Summoned (from your hand) by banishing 1 FIRE and 2 WATER monsters from your Graveyard, and cannot be Special Summoned by other ways. Once per turn: You can discard 1 card to target 1 monster on the field; destroy that target.
If your deck contains many WATER and FIRE attribute monsters, you can set Magical Merchant to send monsters to the graveyard until you get a spell/trap card. The monsters sent to the graveyard can then be used to summon Frost and Flame dragon.
When Skreech is destroyed you can send 2 WATER attribute monsters from your deck to the graveyard, to use as cost for the summoning of Frost and Flame Dragon. Additionally, Skreech is also a WATER attribute monster.
Last Gamble would be useful in a deck that aims to summon this monster. When using the skill, discard FIRE and/or WATER monster monsters. Then, after summoning Frost and Flame Dragon, try to go for an OTK that turn.
Volcanic Shell sounds good for the fire component. Since you can use it to get another Volcanic Shell if it is in the grave, thus giving you more "ammo" to discard while also thinning the deck. You can consider using Brushfire Knight to discard a Volcanic Shell from deck.
As for the water component... Deep Diver can allow you to draw this card next turn. T.A.D.P.O.L.E kind of acts like Volcanic Shell, in the sense that you can get more from deck if it was destroyed in battle. Blizzed can be used if you honestly don't have anything better, since it will let you draw more cards.
Most of the cards I suggested requires to be destroyed in battle though, so you might not want to use them all. And if you do, you'd probably need something to defend yourself. I'd watch out for Ultimate Providence/Divine Wrath too. Those are popular cards these days, thanks to the flourish of effect monsters. All in all, there is probably a reason why Frost and Flame Dragon isn't often used.
When will come the Mokuba-Event again to get a frost and flame dragon? I didn't play the game in this time and i'm trying to get the 3rd king of the swamp out of Generation Next to be prepared for the future, but I don't want to waste my last UR-Ticket for a card from an event.