There have actually been several mermaid cards in Yugioh and they have been quite powerful. Who can forget Cure Mermaid, the cute critter with a solid 1500 attack and an ability that allowed its user to gain 800 life points every Standby Phase. With the recent release of Rising Abyss, mermaid cards are back in the form of the Mermail archetype. Mermail monsters aren’t only a group of mermaid monsters, but include sea monsters as well. They have brought back water-oriented monsters into prominence with their abilities.
Mermail monsters come in three levels: three, four, and seven. The level three monsters are all female aqua type monsters while the level four monsters are all male fish monsters. The two level seven monsters are sea-serpent type monsters. The level three monsters when sent to the graveyard, allow the special summoning of another Mermail monster. Usually, this monster would be a level four, since the level four monsters have effects that can be detrimental to your opponent. For example, Mermail Abysslung has the ability to increase the attack of all water monsters you control by 300. In addition, he makes himself the target of your opponents attacks, which can be helpful considering he has 1800 defense.
The two, level seven, aces of the Mermail archetype are Mermail Abyssmegalo and Mermail Abyssleed. Abyssmegalo is the only that has been released into the TCG and is a huge monster that has 2400 attack and 1900 defense. It can be easily summoned, as its user can discard two water monsters to special summon it. Plus, if its summoned this way, the user can add an Abyss spell/trap card to his/her hand. This is a very easy way to attain the field spell Lemuria the Forgotten City, which is an essential card in Mermail decks. It doesn’t end there; by sacrificing a water monster in attack position, Abyssmegalo can attack twice in one turn!
The Mermail archetype seems very interesting and could produce the same level of success as the Naturia archetype. However, I think Mermail monsters are much more fun to play with so I hope they have a longer run in the TCG. If nothing else, Abyss Rising would be worthwhile buying just to acquire these powerful monsters.