At the time of writing, there are nine cards with paradox
Malicious, Mean, And Scary 97/204 EN.10, Emerald Ink The Song card "Malicious, Mean, and Scary" could also be a good strategy for wiping the board of low-cost enemies
Up the Beanstalk This two-drop uncommon (Peasant) will draw you a card when it ETBs so if destroyed after arrival, you'll never be down a card by investing in it
Not one but two weenies will have to get in the way of this thing, and when they do, an instant speed surveil will crush them and let you fix your deck
Anyone that's ever played with or against RepercussionRepercussion or Toralf, God of FuryToralf, God of Fury should already have some idea of how good this card is, even without the tacked-on hyper-expensive activated ability
The extra part of generating mana of any color gets better if you have changelings, aliens, or doctors