Abrupt Decay - Removes pesky permanents such as Chromatic Lantern, Crucible of Worlds, and more. At first glance somewhat underwhelming but its usages in EDH are considerable given the number of powerful, low cost permanents in the game.
Aetherflux Reservoir - A potential win condition for the deck if the Omniscience, Seasons Past loop has been achieved. A beloved card in many spellslinger decks and a very powerful card used correctly here.
Arcane Denial - Low cost counterspell that reduces grudges by allowing opponents to draw cards. Stops combos to some extent and allows for versatile and reactive play.
Beacon of Unrest - Steals powerful creatures and artifacts from graveyards and puts them to use for your own plans. Situational but often can be very good when reanimating some EDH staples like Sheoldred, Whispering One for example.
Beast Within - A key card in cEDH Seasons Pastigur lists, here it serves as versatile removal and can complete similar functions to its cEDH list if the Seasons Past + Omniscience loop can be completed.
Burgeoning - Allows for ramp on other players' turns from the get go and very good when paired with Life from the Loam for fast ramping for some of the more flashy spells like Omniscience
Chromatic Lantern - Mana fixing rock that allows Tasigur to hit all of his coloured mana requirements on time. A favourite card of mine and a useful piece of utility here.
Circular Logic - Often amounts to a 10+ tax on a counterspell. In rare cases the madness cost comes in, but the deck needs to protect Tasigur and stop other decks from advancing.
Consuming Vapors - Useful for removing pesky creatures and indestructible threats but its rebound makes for a nice hovering removal spell for responding to dangers. (Also its worth noting that I play a lot of 1v1 using this deck as its permitted in my playgroup, so this card does more work there than in multiplayer. For multiplayer, it might be better to run Windgrace's Judgment)
Counterspell - Simple, effective, and useful. Does what it says on the tin and counters a spell.
Cultivate - Land ramp and library thinning. A green staple that sets up later turn plays. Also, best used if delved away in the late game once the basics in the library are gone so that Tasigur's ability can target only vital targets.
Curse of the Cabal - With the Omniscience + Seasons Past loop, can potentially decimate board states. Bonus points if used with Swarm Intelligence to target multiple people at once.
Cyclonic Rift - Bounces all opposing permanents to their owners hands. Sets back opponents and can help you set up your win condition loops.
Dark Petition - A tutor that often nets you three black mana in the process. Used in the Omniscience + Seasons Past loop to return the Seasons Past back to your hand to replay every single spell in your graveyard over and over again!
Deadbridge Chant - My favourite card ever. In this deck and within the meta I play in, this card is used to return random answers to your hand in each of your upkeeps and never fails to amuse with its "Pick a card, any card" style of card selection. Not for everyone but my goodness definitely for me.
Diabolic Tutor - A simple tutor to respond to changes in the board state or alternatively can be used in the Omniscience + Seasons Past loop to return the Seasons Past back to your hand to replay every single spell in your graveyard over and over again!
1x Dimir Charm (GTC)
1x Disdainful Stroke
1x Dissipate (M15)
1x Down
1x Drowned Catacomb (XLN)
1x Fact or Fiction
1x Far
1x Far Wanderings (C16)
1x Fetid Pools (AKH)
1x Forbid (EXO)
1x Forbidden Alchemy (MM3)
4x Forest (ZEN)
1x Golgari Charm (C15)
1x Hinterland Harbor (ISD)
1x Honden of Night's Reach (EMA)
1x Honden of Seeing Winds (EMA)
1x In Garruk's Wake (C16)
1x Increasing Ambition (DKA)
1x Insidious Will (KLD)
4x Island (ZEN)
1x Kodama's Reach (C17)
1x Krosan Grip
1x Life from the Loam (MMA)
1x Llanowar Wastes (ORI)
1x Lonely Sandbar
1x Metallurgic Summonings (KLD)
1x Monastery Siege (C17)
1x Mutilate
1x Mystic Confluence
1x Nature's Claim (IMA)
1x Nightmare Incursion (EVE)
1x Omniscience (M13)
1x Opulent Palace (C17)
1x Overgrown Tomb
1x Paradox Haze (TSP)
1x Perplex (RAV)
1x Phyrexian Arena (CN2)
1x Praetor's Counsel
1x Putrefy (MM3)
1x Reality Shift
1x Regrowth (DDL)
1x Rewind (MM3)
1x Search for Tomorrow (IMA)
1x Seasons Past (SOI)
1x Silence the Believers (JOU)
1x Sinister Sabotage
1x Splendid Reclamation (EMN)
1x Sultai Charm (KTK)
1x Sunken Hollow (BFZ)
4x Swamp (ZEN)
1x Swarm Intelligence (HOU)
1x Tainted Isle (PCA)
1x Tainted Wood (C15)
1x Tasigur, the Golden Fang CMDR
1x Temple of Deceit (THS)
1x Temple of Malady (JOU)
1x Temple of Mystery (THS)
1x Torment of Hailfire
1x Training Grounds (ROE)
1x Tranquil Thicket
1x Tribute to the Wild
1x Underground River (C16)
1x Urban Evolution (MM3)
1x Urborg, Tomb of Yawgmoth
1x Villainous Wealth
1x Vona's Hunger
1x Watery Grave
1x Woodland Cemetery (ISD)
1x Yavimaya Coast (ORI)