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.