There are few decks in Legacy, and even in Magic in general, that are as complex as Doomsday. Doomsday is a card with an enormous cost that gives you access to anything you could possibly need to win the game. The problem is that there are near infinite combinations of cards in different orders and a razor thin edge between winning the game and leaving yourself dead. If you can work through the permutations enough or memorize enough piles to begin to extrapolate for specific situations, what you get is a monstrously powerful and resilient combo deck. Let’s take a look:

Doomsday ? Legacy | g0ld_rook, 5-0 Legacy League

• Creatures (1)
• 1 Laboratory Maniac

• Spells (43)
• 1 Ideas Unbound
• 1 Rain of Filth
• 2 Abrupt Decay
• 2 Lotus Petal
• 3 Burning Wish
• 3 Cabal Therapy
• 3 Doomsday
• 4 Brainstorm
• 4 Dark Ritual
• 4 Duress
• 4 Gitaxian Probe
• 4 Lion's Eye Diamond
• 4 Sensei's Divining Top
• 4 Ponder

• Lands (16)
• 1 Island
• 1 Swamp
• 1 Badlands
• 1 Tropical Island
• 2 Bloodstained Mire
• 2 Flooded Strand
• 4 Polluted Delta
• 2 Underground Sea
• 2 Volcanic Island

• Sideboard (15)
• 1 Cabal Therapy
• 1 Doomsday
• 1 Empty the Warrens
• 1 Emrakul, the Aeons Torn
• 1 Infernal Contract
• 1 Karakas
• 1 Massacre
• 1 Shelldock Isle
• 1 Tendrils of Agony
• 1 Tropical Island
• 1 Void Snare
• 2 Abrupt Decay
• 2 Xantid Swarm

Buy This Deck

The first interesting thing about the maindeck is that there are zero copies of Tendrils of Agony. This means that in game one, you either need to generate enough mana to resolve Burning Wish to get a copy of Tendrils of Agony, or go for Laboratory Maniac kills. Out of the sideboard, you have access to all manner of goodies. Tendrils of Agony and Empty the Warrens are powerful Burning Wish targets, while Shelldock Isle plus Emrakul, the Aeons Torn gives you a slower combo kill that crushes control decks.

The idea here is relatively straightforward. You’re looking to use Sensei's Divining Top, Ponder, and Brainstorm to dig your way towards fast mana like Dark Ritual and Lion's Eye Diamond, disruption, and Doomsday, with Burning Wish being able to stand in as any of the missing pieces. Once you’ve ripped your opponent’s hand to shreds with Duress and Cabal Therapy, you can cast a Doomsday.

Here’s where everything starts to diverge based on how much mana you have, what’s in your hand, and what you know about your opponent’s hand. The most straightforward pile looks something like this:

Ideas Unbound

Laboratory Maniac

Dark Ritual

Gitaxian Probe

Gitaxian Probe

This pile only requires you to have four mana, UUUB, to be able to draw and cast Ideas Unbound, then Laboratory Maniac, followed by Gitaxian Probes to win the game. If you have an extra Blue mana and a cantrip, you can even draw into the {card]Ideas Unbound[/card] immediately and win on the spot. However, things get more complicated if you have a Sensei's Divining Top, since top adds a card to the top of your deck every time you draw a card with it.

This means that our original pile either costs more mana, since we’ll have to redraw and recast Sensei's Divining Top several times to draw the whole deck, or that you’d have to fit something like Brainstorm into the pile that can still get your deck empty, if only for a moment. However, Sensei's Divining Top is also a powerful card in these situations because it gives you extra ways to try to trigger Laboratory Maniac at instant-speed, effectively shutting off some removal spells.

This is already getting overwhelming for me, and we haven’t even touched on what happens when you have to squeeze a discard spell into your Doomsday pile or how you might go for a Tendrils of Agony kill instead of Laboratory Maniac. The deck is second to none on the complexity scale, and but if you can work your way through all the combinations in a reasonable amount of time, there are few combo decks are resilient and explosive as Doomsday.