Coming to you from the horribly combined depths of Shockwaves of the Shattered Rainbow, I present:
Melnia, the Aqua Shadow!
Now I know that I don't even own any cards from this set, and in my mind the idea of hybrid, multi-civilization and multi-race creatures is a bit kinky. Still, this is one of the better ones. And besides, look at all the pretty colors on the rainbow card! Like some of the other new creatures introduced in Shockwaves, Melnia is put into the battle zone tapped. While this may make it seem like easy prey to enemy creatures, with is its low Mana cost and strength, it has a trick up its sleeve: Slayer. A cherished Darkness ability, this lets it destroy the enemy attacker if Melnia loses a battle and is itself destroyed. Also, it cannot be blocked. So if your opponent is attacking Melnia, they are barking up the wrong tree.
A good deck to put it in would be a mixed Darkness/Water deck: specifically, one that has equal parts destroying and tapping spells. Take Virtual Tripwire, for instance. Send Melnia in on the second turn, and leave it to endure Summoning Sickness. Only a very stupid opponent would attack it now. Then, on the next turn, play Virtual Tripwire to tap an enemy creature, since creatures cannot attack untapped enemy creatures. Melnia will most likely die, but so will the creature it attacks. Or, you can just get four Melnia in a deck, the maximum amount, and just suicide them against big tapped creatures or Blockers later in the game. And it looks pretty darn awesome in addition.
Ballom's Rating: 3/5. While Melnia is good in a particular field, its low strength, in comparison to its small Mana cost, means that it can't accomplish too much.