Paradox Engine
Oracle Text
Whenever you cast a spell, untap all nonland permanents you control.
Card Rulings
2/9/2017 Paradox Engine’s triggered ability resolves before the spell that caused it to trigger. The ability will resolve even if that spell is countered.
Seriously, consider what is out there. Azami, Kydele, Captain Sisay, Kaho, and either Selvala can easily start spinning towards near-infinite chains.
That's not even counting commanders that just have "good" tap abilities like Hannah, Krenko, Kiki-Jikki, Muzzio, or Yisan.
Dear sweet god.
So... yeah. Mostly good for cards with green or blue card draw/search options, though some some commanders (like Krenko and Kiki-Jikki) can still break the game with this thing.
Sigh...kinda disgusted with this, honestly. Lazy design.
This card will be played and is powerful, but as I said, Sharuum combos are way easier to pull off. First you need this card +1. Captain Sisay/Demonic Tutor/etc. would need to find this card for you, because you will rarely just luck draw this card (or any 1 card in EDH) +1 card again. You need something to draw you cards to keep feeding spells into it, let's say Arcanis the Omnipotent is another +1 card. Then you will need a bunch of mana rocks already, extra turn permanents and/or a way to untap your lands (Candelabra of Tawnos or Magus of the Candelabra) +a few. So you are already in the 5+ card range to go infinite. So many combos like this exist and will not be banned. Shoot, even Retreat to Coralhelm + Ruin Ghost will be banned before this.
Prophet of Kruphix generates absurd amounts of advantage on its own, without anything else required on the board. Of course you cast cards through it, but it's a one card engine.
This card requires a whole bunch of board state in order to be properly utilized. Keep in mind you need to keep casting spells in order to power it, so if you have no mana rocks or mana elves, you'll have much more trouble utilizing it properly.
This means that one Pyroclasm or small cmc removal will leave this card alone and doing nothing.
You need fuel for this card so
Arcanis the Omnipotent, Urza’s Blueprints, Temple Bell and friends are what you would need to break it.
B. Spells cast through Isochron Scepter can still be countered, while triggered abilities can only be countered by effects like Stifle.