Well, basically in this semi-regular collumn, I'll talk about the Top Five of the Worst X of Set Y. The majority of these cards are not used in competitive decks...full stop, but can be fun and/or marginally effective on a lower level.
Anyway, with the brief introduction out of the way, let's get down to it!
Counterlash (4UU) Instant
Counter target spell. You may cast a nonland card in your hand that shares a card type with that spell without paying its mana cost.
Now, this looks kind of...underwhelming to begin with. However, during a Limited game, I saw someone use Counterlash to stop a Flashbacked Lingering Souls, to much mocking - the player had an Increasing Devotion in his deck that he would have thought any counterspell would have been saved for. They shut up when he played Alpha Brawl and wiped his opponent's previously glorious-looking field of Spirits into nothing. The message was clear - in a Limited U/R deck, this card can do some serious mayhem with the plethora of higher-CMC Creatures and Sorceries that can be harder to get out.
Alpha Brawl (6RR) Sorcery
Target creature an opponent controls deals damage equal to its power to each other creature that player controls, then each of those creatures deals damage equal to its power to that creature.
Yeah, speaking of Alpha Brawl...despite its unbelievably high CMC, this card can and has completely reversed some games, as it's normally a complete board wiper, or at the very least gets rid of the major and some minor threats. However, because of the CMC issue, it's much lower on this list than it could have been. Then again, any lower (I'm thinking CMC6?) and it'd be in Mythic range.
Curse of Echoes (4U) Enchantment - Aura Curse
Whenever enchanted player casts an instant or sorcery spell, each other player may copy that spell and may choose new targets for the copy he or she controls.
It's no secret that I love me some curses, and this one's one of my favorites. If you sideboard it in against a Burn deck, it helps you keep tempo, and I saw one game where a mirror-match of GU Self-Mill turned into a one-sided victory for one player as he sideboarded this card in and just copied all of his opponent's Dream Twists and Forbidden Alchemy's to mill himself faster than the other player did. Severly underrated.
Sudden Disappearance (5W) Sorcery
Exile all nonland pernaments target player controls. Return the exiled cards to the battlefield under their owner's control at the end of their next end step.
It gives White Weeny a much-needed mass Evasion card. However, the reason this card is on here is tentative - could a judge/rules guru please tell me if this is right - doesn't this basically read: Destroy all tokens? If tokens cease to exist once they leave play, doesn't that mean, well...they go away forever once you drop this? With the Token metagame growing stronger, this could be an affordable replacement for a budget deck as opposed to Day of Judgement.
Dungeon Geists (2UU) Creature - Spirit
Flying, When Dungeon Geists enters the battlefield, tap target creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control Dungeon Geists
This card...wins games. For four mana, you get an Arrest-style ability and a 3/3 body with evasion. Even if the creature gets untapped by other means, it can't untap during untap step afterwards, so there's very little tricky stuff that can be done. This is a very, very underrated rare and should be in some Spirit decks.
Well, that's all for now. If anyone's got any comments or suggestions, please say so. Cheers, and have a nice week.