Seismic Assault and Swans of Bryn Argoll form one of my favorite combos in Magic. I’m in for any excuse to put extra lands in my deck, and turning them into Shocks is good enough, but turning them into Shocks with the added possibility of comboing your opponent out as early as Turn 4 is a dream.
Most of the time you see this combo placed into a list with Treasure Hunt and a very high land count in order to assemble the combo as quickly as possible, but that build has obvious issues with including some interaction for other combo decks and in being resilient to the powerful disruptive elements in the format.
But when you look at the two combo pieces, they are both fine individual cards. Swans of Bryn Argoll is an efficient body that gives you the ability to turn the corner quickly and turn your burn spells into additional card draw in control mirrors. Seismic Assault is a game-breaker against creature decks like Humans and Affinity, giving you a near-endless supply of cheap removal to buy time until you finish them off with a combo turn.
So why not put these cards into a U/R Control shell, which has been looking for a solid combo finish since Splinter Twin was banned? I’m no fan of Through the Breach plus Emrakul, the Aeons Torn or Kiki-Jiki, Mirror Breaker plus Deceiver Exarch, but I can get behind some Swan-Assault. (Disclaimer: This should in no way be interpreted as an incitement to physically harm actual swans.)
The surrounding pieces are all typical control cards. Some red sweepers make their way into the maindeck because the current metagame is creature-heavy and sweepers play well with Swans. The Dakmor Salvages let you keep the chain going no matter what you draw, and the singleton Kozilek, Butcher of Truth ensures you’ll never deck yourself or run out of lands to chuck at your opponent’s head. Heck, with a 27-land deck, you may even cast it a few times.
The mana requirement of a triple-red card in a primarily blue deck is the main downside here, but Cascade Bluffs pulls a ton of weight, and it’s not like you need to cast Seismic Assault on Turn 3 much of the time. As someone who is typically conservative with mana consistency, I’m much more excited about getting a real combo in my U/R deck than I am about making its mana worse.