Strength lies in numbers. Such is the myr way. While none of these cards are powerful on their own (except four), all of them are united by the same strategy: make a lot of myrs, strengthen them beyond reason, and then give hell to anyone without an aetherize. When playing a myr deck, you are amassing an army, constantly expanding it and making every other player nervous. Remains my main deck.
The first thing to do is have three lands (or two lands and a gold myr). The next thing to do is whatever you want. Here are some individual card descriptions, to get you started.
Plains: Tap these for mana. This deck is one-color-fits-all.
Gold Myr and Palladium Myr: Mana ramp. These folks will mostly be used as lands, with the benefit of an additional blocker or attacker when the time comes.
Myr Reservoir: The reservoir can be used for mana, but it's most important ability is to bring dead myrs to your hand. Note that you can't use its mana for Tempered Steel, Dispatch, or Obelisk of Urd.
Myr Turbine: The other myr artifact. Endlessly spawns myr, until you have five to spare. At that point, you can tap those five myr to search your library for a myr creature. Unless there's a reason not to, you usually want to go for the battlesphere.
Myr Servitor: Zombies. If one of them is still around at the start of your turn, then so are the rest of them. As soon as you put the second one on the battlefield, you get an infinite disposable blocker. If you have the three to spare, things just get silly.
Myr Enforcer: Seven mana for a 4/4? Who would play such a card? I would, that's who. Because of how many myrs you can pop out, the cost quickly drops (one for every artifact). If you draw it late game, you can usually summon it for free. If it costs any more than three mana, you're being ripped off.
Myr Superion: Two mana for a 5/6? That's absurd! Yeah, it is a bit crazy. When you have two mana from creatures, you can just summon this guy and laugh at everyone's dismay. Note that if you start with a Palladium Myr, you're guaranteed to be able to use the Superion.
Obelisk of Urd: Now we get to the buffing cards. These cards make your creatures beefy. If you have an army of little dudes, a couple buffing cards can suddenly swing the game wildly in your favor. This specific buffing card gives your dudes +2/+2. It's better later in the game when you have creatures you can tap for mana. Note that "each creature you tap while casting" pays one mana, so a Palladium Myr will pay for three mana and a Gold Myr will pay for two.
Tempered Steel: Another buffing card which gives +2/+2 to all your creatures. Cheaper and therefore better under most circumstances.
Myr Galvanizer: Tired of buffing cards which can't also punch things? So am I. The main effect of Galvanizers is to give other creatures +1/+1. They also have the ability to untap all your other myrs, which can be very useful.
Darksteel Myr: It's indestructible. Early in the game, if you have no buffing cards out, it's useful only for blocking. Later, when all of your creatures have +5/+5, it becomes an unstoppable killing machine. Always nice to have on the battlefield.
Hovermyr: A cheap little thing which flies and never rests. If your opponent has flying creatures, it can be an invaluable blocker. If nobody else has flying, it can peck. Attack someone every turn. Peck at them so that they are more vulnerable when the time comes. And, of course, the pecks just get bigger as you buff your creatures.
Dispatch: This lets you exile a creature for one mana. Excellent for removing those pesky folks who are messing the balance of the whole game. NEVER USE IT WHEN YOU HAVE LESS THAN THREE ARTIFACTS. That would be dumb.
Myr Battlesphere: The star of the show. Remember when I said there were four powerful cards in the deck? These are those four cards. At seven mana, it is by far the most expensive thing here, but it is completely worth it. It comes in with four little 1/1 myrs which, by this point in the game, are probably buffed to 5/5s or higher. Also, when it attacks, you can tap creatures to increase its attack and, more importantly, to deal automatic, inescapable damage to the defending player. This card is a lathe on which to carve empires. It has won me many a game.
The Infinite Combo: This deck isn't at all built around this, so don't make "getting the combo" your one and only goal in the game. Still, I'd hate for anyone to miss an opportunity if they had the cards. For this combo, you will need the following: 2 Myr Galvanizers and 2 mana worth of Gold or Palladium Myrs. If you tap all of your mana ramping myrs, you get a bunch of mana. Then, tap a Myr Galvanizer, using one mana, to untap all other myrs. Then, tap all of your mana ramping myrs again, to get all that mana a second time. Tap the second Myr Galvanizer with one mana to untap everyone again, including the original Galvanizer. Repeat as desired. You have infinite mana.
On the sideboard I've put cards which are cool but that I didn't like personally.
Shimmer Myr: Has flash, and gives all your artifact cards flash. It could be incredibly powerful in the hands of someone who knows how to use it. I do not know how to use it.
Myr Welder: Myr welder can be tapped for a little ability called imprint. What does it do? Oh, nothing much, it just EATS THE CORPSES OF ENEMY ARTIFACTS TO GAIN THEIR POWERS. Well, I suppose technically it welds their parts to itself, rather than eating them. Still, it's cool. Use it against artifact-heavy decks.
Lodestone Myr: A 2/2 which gets +1/+1 for creatures you tap. Not useful for much except The Epic Combo. After a while of never getting the combo, I decided to remove the Lodestone Myrs. The Epic Combo was not meant for me, apparently.
The Epic Combo: Requires that you have a Lodestone Myr in the deck. For this combo, you will need the following: 2 Myr Galvanizers, 1 Gold or Palladium Myr, 1 Lodestone Myr, and any other creature. First, tap the "other creature" to give the Lodestone Myr +1/+1. Then, tap the mana myr for mana. Then, use this mana and tap a Myr Galvanizer to untap all myrs. Then, buff the Lodestone Myr again. Then, tap for mana and use the second Myr Galvanizer to untap everyone again. Repeat as desired. You now have an infinity/infinity with trample.
That's it. Hope this was helpful!