In the first version of my cube, I had pretty much put together a stack of cards I wanted to play with and I thought were fun. Among them, one of the most wacky cards in Magic: Platinum Angel.
In our first drafts, it was nearly an "I win" card. T
he control deck that drafted him was always sucessful, he was always a 1st pick, so whoever opened him played control, and so on. It was not simply a hype, he did win several games by himself. When he hit the board, we would often have a watcher go through the other player's library to check if he had a way to deal with the Angel. If he didn't, that player simply conceded, which happened too frequently.
The wacky and fun card that I had pictured grew to be hated because it was deemed unfair. I studied the drafted decks a bit and found what made Platinum Angel, which was never a great card in constructed, the most sought after card in the cube: not all decks had removal that could target him, and most had very few. White had m
ostly Pacifism-like enchantments and Wing Shards-like attacker removal. Red had to combine two or three small burns. Blue could only counter the Angel. Green and Black were the only ones to have a reasonable amount of answers, but distributed among all players it was not enough. This illustrates how a limited environment can be unbalanced by a mistake in the proportion of utility cards.
With this issue in mind, I added cards that dealt with the Angel to all colors. Green already had some artifact/enchantment hate and got more, like Viridian Shaman and Wickerbough Elder. White got Disenchant and Ray of Distortion to fill the same roles as green. To the other colors I added more generic cards: red got artifact hate (Manic Vandals, Demolish) and stronger burn that could take 4-toughness creatures by themselves, like Lightning Blast. Blue got creature bounce such as Aether Adept. Black got more creature removal such as Faceless Butcher and Rend Flesh.
After these changes, Platinum is not a format defining card anymore, as it once was, and it is much less hated. One can use it as win condition if backed up by a suite of counterspells, but it acts mostly as an afterlife, or a threat-that-has-to-be-answered. It also still flies and deals 4 damage a turn when unblocked, so it's not a terrible deal. Today it is a much fairer card than before, and its very existence is great for deck building: it reminds you to always check if your deck can lose to a single card.