Burning Tree-Emissary and Manamorphose are currently amongst the best enablers and if Wizards ever makes the mistake of printing a similar card to Manamorphose this would be one of the first cards I would be looking back at
Take control of opponents creatures and turn them against their owners in Mindbug, a new card game co-designed by the creator of Magic: The Gathering - Richard Garfield
However, there are some cases where the rule of one card copy per deck can create even more adverse situations Circu, Dimir Lobotomist Circu, Dimir Lobotomist, oddly enough, can be viable in play, even without using its last ability to stop casting cards with the same name as the exiled cards
Gempalm Incinerator Illus
Drawing a lot of cards is something that can really flip a game on its head, especially since it relies on your opponents drawing cards and attacking to give you value
Christmas Playmat