This is an updated and improved version of a deck idea I had right around the release for fifth dawn. It's a highly synergistic combo/control deck that uses a variety of control elements to create incremental advantage until your combo can go off, or your counter generation becomes overwhelming on its own.
Land Disruption: Quicksilver Fountain and Power Conduit combine to disrupt your opponent's mana base while generating counters for your use. Quicksilver Fountain permanently turns your opponent's lands into islands, because its clearing ability will never activate as long as you are removing counters from your own lands with Power Conduit. This is a major headache for non-blue monocolor or multicolor decks. You can either use this engine to pump up your creatures or speed along the progress of a Darksteel Reactor. As a result you always have a solid aggro output for your counters, and a serious threat with the Reactor's win condition.
Counterspells: The deck runs Remand as a counter because of the draw ability. The infinite combo is a little clunky, so cantrips are important to include. It's a fine counter on its own, but throwing it onto an Isochron Scepter can be downright mean if you find yourself waiting to draw your win conditions.
Other control elements: Prodigal Sorcerer and Cathartic Adept primarily exist in the deck as outputs for your infinite combo, but both offer some form of control until that happens. Milling is prophylactic removal, and stinging your opponent's small creatures or removing loyalty from a planeswalker is always worthwhile.
Draw Spells: In addition to Remand, the deck runs both Serum Visions and Opt to generate card advantage. Cheap and reliable, they help find the whatever pieces you're missing. Opt can also be thrown on an Isochron Scepter in the event excessive digging is necessary. It's actually possible to assemble the engine of the infinite combo without a win condition present, and if this is the case, you can use this pairing to draw infinite cards to remedy the situation.
The Combo: The kicker that makes the deck interesting is an infinite mana combo through Isochron Scepter/To Arms!, Synod Artificer, and Life and Limb. Life and Limb makes it so that casting To Arms! from the Isochron Scepter untaps any lands used to cast the scepter's ability. Synod Artificer then untaps the scepter, and will itself be untapped by the next casting of To Arms!. That's your infinite mana source, but any creatures with a tapping ability can be caught in the same loop, and that's where Coretapper combines with Darksteel Reactor, Cathartic Adept instantly mills your opponent, or Prodigal Sorcerer deals infinite damage.
If the combo never drops, usually the pieces you're left with can be threatening all on their own. Coretapper, the counter generation from the fountain and conduit, and a Darksteel Reactor on the table can run down the clock on a game in short order. And if you have a Remand on a scepter and the opponent's mana base is toast from the fountain, you're likely able to wait out the game while they're unable to play most cards in their deck.
I'm always looking for advice! I'm a returning player who has missed every set since Fifth Dawn, so there are a LOT of cards I simply don't know about. Previous versions of this deck were only legacy legal, due to the use of Toymaker, Ambush Commander, and Vitalize for the infinite combo, but I've finally found a modern legal replacement in Synod Artificer, To Arms!, and Life and Limb.
