Every so often, Wizards prints a card that is all five colours, usually striving to make the card powerful or striking because of this. Some of these cards are kind of okay. Some of these cards are substantially less okay.
The first 5-colour card ever printed was Sliver Queen, back in Tempest. When I started playing, it was still the only card of this sort in existence, so it was kind of a big deal. Like any other human being for a stretch of time directly following the Rath block, I wanted to be the "Slivers" guy, which means that I wanted to run a deck with every single Sliver in it, and I would have given at least one of my friends' eyeball for a Sliver Queen. I looked at pictures of Sliver Queen on the internet, because back then we didn't have all those fancy Magic sites with actual articles or anything, by which I mean that I didn't know they existed.
The next quintuple chromatic card to stumble along was Coalition Victory, which was kind of cool because it made you win the game, plain and simple. Granted, by the time Invasion block rolled around, the concept of playing removal in response really hadn't clicked in with me or my friends... so we had yet to realize it would never work in the real world. The mana cost is also probably the worst in the game. But you could put it in your slivers deck, which was naturally five colors with no mana fixing, since, hey; you were already playing permanents of five colors, and you still didn't have a Sliver Queen.
Two sets later came along the lovable Cromat, whom one can't help but love for having a dozen-odd activated abilities. Interestingly enough, Wizards had a Popularity Poll for all the Legends a while back, and Cromat managed to win for no conceivable reason. Seriously, he looks to possess animal intelligence, at best... and he managed to even beat out the heavily-favored Squee. Cromat has literally no place in the story. It just goes to show, Wizards really needs to wise up to the idea that most people like the flavour of the game but don't give two dangs about no Gerrard.
Last Stand is a sad waste of a good card name. Seriously, if I'm going to lay down a five-colour sorcery, I might as well just use Coalition Victory and win the game.
Atogatog must die. Let me say I'm a big fan of tribes that are only going to be supported heavily for one set getting a lord, preferably a lord that really plays up their abilities rather than one that just gives them +1/+1 or whatever. This card, however, is not a good lord. He is possibly the worst lord card ever printed. If you're playing an atog deck, you sort of feel like you should be playing their lord, which is one of the worst creatures ever, so he leads to moral dilemmas as well as lost games. An experiment: build a deck that includes Atogatog, but not Dragon Gate. I guarantee you that the deck will be better if you replace the Atogatog with a Sliver Queen, even if the deck contains zero other Slivers and many Atogs. Even if the deck contains Plague Sliver. Atogatog is just so bad, and he's not even cool. He's lame. In fact, I've said this all before. Like, four days ago.
Karona, False God and Sliver Overlord were probably designed by different people on the opposite sides of a cubicle wall. The Overlord isn't nearly as awesome as the Queen, but he's still a 7/7 beatstick and his first ability is pretty good. Karona, meanwhile, is a mess. An important story character (or so I'm told,) and yet she has 2 less power and toughness than the Overlord, and costs one mana more. Oh, and she swaps over to your opponent each turn. Why the creature-type pumping, meanwhile? Tribal decks typically stick to one, maybe two colours. So you add three or four colours more to support Karona. Your opponent essentially gets a Karona too, meanwhile, without having to play it or even deviate from his mana base. I weep. A 5/5 creature that gave all of your creatures +3/+3 all of the time that cost WUBRG would still probably not be competitive. At least she doesn't have stupid art, which gives her an advantage over Atogatog, and if you can actually play her in Limited, you'd probably win or at least draw a removal spell.
After that pair of winners, Wizards put off any more five-colour madness until Kamigawa, in which we were graced with Genju of the Realm. He's actually pretty neat... he has a goofy card type (enchant land,) and is pretty hard to stop if you do manage to get it into play. Most decks can't handle a sorcery-proof black 8/12 trampler more than once. I sort of wish they had loaded him with more random abilities, but what can you do.
Transguild Courier is all five colours without being WUBRG. I actually like him because he could probably be any rarity and not seem out of place. It's really simple and pleasant to have around in limited, so it could be common. It has a striking and unique ability, so it could be rare. I use him in my Scarecrow deck to fulfill colour requirements without being a bitch to get in play.
Scion of the Ur-Dragon is the smallest of the five-colour creatures. I realize that Sneak Attack is too good, but making it all five colours and more vulnerable to destruction is not the answer. I would really rather have Sneak Attack. Like, really really.
I don't particularly like Sliver Legion. I understand the sentiment - it's the next logical step in crazy Sliver synergies - but it doesn't feel like another Sliver boss. It feels like a bunch of pastel slivers. Seriously, guys - my whole deck is a Sliver Legion.
Horde of Notions and The Reaper King are what one-set-tribe lords should be (if they're going to be stupid 5-colour things just because their tribes are 5-colour.) Horde of Notions is a terror in combat, and his ability plays extremely well with the fact that in Lorwyn, basically every greater elemental had a CIP ability and an easy way to get into the graveyard. It's cool, and it synergizes with what the tribe is doing without being a form-letter lord.
Same with the Reaper King. In fact, the Reaper King is also one of the coolest creatures around. He looks like one seriously badass dude, and there is no ability more intimidating than "Destroy target permanent" without an activation cost of any sort in front of it. Tribal Scarecrows is probably going to be pretty bad, but tribal Scarecrows with the King in tow is a lot cooler, even if it's still bad. I love the Scarecrows conceptually as well as visually, and I know they're not going to get any more support after this block, so might as well stock them up with a seriously cool lord.
Nevertheless, I still like Sliver Queen more.