There are a number of published UR decks out there, this is my take on them. I've done a small amount of testing so far but I'm at around 50% success rate and doing well enough to keep at it.
The deck is far from grindy but it isn't fast. You burn their creatures with Lava Axe and hit them with tempo plays like Just the Wind while your opponent builds up Fevered Visions damage. The deck provides copious card-draw opportunities and you can easily do 9-15 damage to your opponent using recursive Fiery Impulses. Goblin Dark-Dwellers, Thing in the Ice, and Jori En take up the slack with combat damage.
Creatures:
Jace, Vryn's Prodigy: loots for us early and recasting a either of our madness enablers once he flips is sweet.
Goblin Dark-Dwellers: See Jace. Note, GDD casts the Lightning Axe without discard if you want him to, otherwise the Dark-Dweller provides a nice ground body/cover mid-game and can slow some threats.
Jori En, Ruin Diver: A one-of because we're casting lots of spells and the extra card draw is a nice trick. Not a core piece of the deck and though I've never regretted an opportunity to cast her, I also rarely miss her. She in combination with Fevered Visions is almost card-draw overkill, though I've never come close to decking myself.
Thing In the Ice: More than anything, Avatar Aang is a great honeypot. Opponents sit and watch it shrink and hold up mana to deal with it. Flipping Thing is not vital to the success of the deck - it's a great blocker for Sylvan Advocates and the like in the early game and every now and then you get it to flip and do some big damage in a single turn.
Planeswalkers:
Chandra, Flamecaller: Aside from Just the Wind, her ability to wipe out small creatures is our only real defense against a flipped Abbey. Otherwise, Chandra is just one of the best planeswalkers in the format.
Spells:
Fevered Visions: This absolutely wins games, particularly in multiples. Even when it isn't though, the low curve and the high quantity of spells in the deck always result in a high reward for gaining the extra cards per turn. If you have a play you could make but don't have to - keep in mind that there are enough instants and sorceries in the deck that you may end up with something nice to play on your opponents turn if you leave mana up.
Tormenting Voice + Lava Axe represent our Madness enablers, helping to find us cards or shut down Thought Knot Seers and the like.
Fiery Temper + Just the Wind are our madness payoff cards. Note, Fiery Temper to the dome is almost always the right decision, particularly if you have your Fevered Visions going.
Magmatic Insight might go - at 25 lands we see a lot of them, and late in the game it's easy to dump tap lands or Shivan Reefs for value. Still, it might make more sense to drop to 24 lands and find a replacement card for this slot.
Land:
I limited to five tap lands in four Wandering Fumarole and one Highland Lake. I think I've activated Wandering Fumarole once since I started playing the deck - using it is not a core strategy.
Shivan Reef is a necessary evil. Once you have two mountains and two islands, use this for Magmatic Insight food. You shouldn't need to take pain at this point unless you are making a big "one turn" Thing in Ice flip late in the game (this is doable).
