I’ve been doing a ton of triple Mirrodin Besieged drafting on Magic Online lately, and I’ve been winning my fair share of packs. Triple MBS is a limited-time draft format, so there likely won’t be much strategy written around it. Triple MBS is a great format to draft because it’s a small set (less packs opened) and because it has relatively more money cards than Scars of Mirrodin. Okay, onto some thoughts.
First, I don’t think infect is a very good strategy in triple MBS. The infect cards are spread out across too many colors, so getting a deck together is tough. Second, the best infect cards are also the best cards against infect. Blight Widow and Priests of Norn will be highly picked by everyone, so you’ll end up with the drecks, like Flensermite. Third, infect is a popular (but bad) strategy, so the cards will be that much harder to come by.
Fangren Marauder is first-pickable. I’ve not had any trouble picking up a full playset of these in most of my drafts, and I’ll always splash green to play them. They are the nuts against non-infect decks, and they are even great against infect. Next, anything that gives a -1/-1 counter or does one damage is playable, and probably will be awesome in your deck. Any guaranteed 2-for-1 is playable (even Myr Sire). Sword of Feast and Famine isn’t nearly as threatening as you think – it’s a mana sink in the early turns, and every deck should have an answer to it (maindecked, none the less). There are far fewer mana fixing cards to make splashing three colors easy in triple MBS than there are in Scars (no mana Myrs), so Sphere of the Suns is a great pickup, as well as Viridian Emissary.
So, what do I think is the most playable strategy in this format? Red-Green artifact sacrifice. The core of this deck is anything that works with artifact sacrfice – Fangren Marauder, Gnathosaur, Ichor Wellspring, Myr Sire, Kutholda Flamefiend, Myr Turbine, Spine of Ish Sah, and such. Red in general has powerful cards all along the curve, and the synergy that can be put together in with this core of cards is amazing. In general, I’m very open to also splashing white in these colors, for things like Master’s Call, Divine Offering, Priests of Norn, and Choking Fumes. If you happen to open a Spine of Ish Sah, try your hardest to get a Treasure Mage, and pick Gnathosaur high.
I highly recommend triple MBS drafting to anyone that has such an inclination. It’s a great format that won’t be around for long, so enjoy it while you can!