Ad Nauseam Tendrils

This is my Legacy deck. I've played a lot of different decks, but I keep coming back to this one because it always presents an interesting puzzle.

Much has been said about the theory behind this deck. Key points:

• Combo decks in Legacy need to be resilient or have a back-up plan. The way that many decks do this is through powerful cantrips (Brainstorm, Ponder, and the like). You then add a secondary plan (e.g. Elves has a midrange beatdown line) or additional resilience through disruption and/or speed. Ad Nauseam Tendrils opts to use discard as its resilience. As other examples, Show and Tell decks use countermagic, Dredge uses speed, etc.

• At the heart, you are a big-mana combo deck. You need to assemble a critical mass of spells that produce mana and find other spells such that you can cast a lethal Tendrils of Agony. This is typically pretty trivial, assuming that you know how to play through your opponent's disruption.

• Your ratios for the maindeck are pretty solidified. You want:

  • 30-31 mana sources
  • 15-16 cantrips/filter spells
  • 6-7 interactive spells
  • 7-8 business spells

• When sideboarding, you want to modify your maindeck by siding out elements that are bad and replacing them with good elements. That's a broad statement, but generally applicable. You usually end up tweaking your ratios to each matchup. Examples:

  Miracles: You want to kill them quickly, reduce your effective necessary Storm count, and draw a billion cards to make sure you always have gas. Discard is not at its best (they often try to float countermagic on top of their library or lean hard on Counterbalance; Flusterstorm beats the former line). Keep Counterbalance off the table and eek out advantages with Dark Confidant (he effectively draws you two extra cards every turn; the attack for 2 is 1 less spell you have to cast for Tendrils of Agony).
  In: 4 Dark Confidant, 3 Abrupt Decay, 2 Flusterstorm
  Out: 1 Swamp, 1 Cabal Ritual, 2 Preordain, 2 Cabal Therapy, 1 Duress, 1 Grim Tutor, 1 Sensei's Divining Top

  Show and Tell: Keep Sneak Attack off the table. The way that they beat you is through the stack; use your Flusterstorms to fight that angle. Discard should be pointed at their combo pieces (unless you have the cards to go off, in which case you should be hitting their countermagic/cantrips).
  In: 2 Chain of Vapor, 2 Flusterstorm, 1 Echoing Truth
  Out: 1 Cabal Ritual, 1 Sensei's Divining Top, 1 Swamp, 2 Cabal Therapy

  Death and Taxes: Thalia, Phyrexian Revoker on Lion's Eye Diamond, and Batterskull are the only cards that you really care about. The fact that two of these are X/1s is a huge boon to your strategy. Duress is an easy cut, since they don't have non-creature spells that you care about except for Batterskull.
  In: 2 Dread of Night, 1 Massacre, 1 Chain of Vapor
  Out: 3 Duress, 1 Sensei's Divining Top

• Notice that you cut Swamp a lot. It's the worst mana-source in the deck, and you should always look to cut it against non-Wasteland decks.

• Brainstorm is objectively the most powerful spell in the deck. You should always think about how you can best use it in a given matchup: hedge against spot discard, find missing combo pieces, put extra pieces back and shuffle them away with a fetchland.

• Infernal Tutor has a lot of tricks that you can play with it. The most important one (that makes the deck tick) is maintaining priority while casting it and cracking Lion's Eye Diamond. Hellbent checks on resolution of the spell, thus turning this combo into an effective Demonic Tutor + Black Lotus. However, you can do other things. You can apply the above scenario to any Instant in your hand, including casting Rituals (there are lines where I've had to do this to play around Vendilion Clique). You can also fail-to-find with the "first mode" of Infernal Tutor, just to get an extra card out of your hand. Also, never forget that chaining Infernal Tutors is a path to victory; you don't have to cast Past in Flames to win.