iMtG Server: Gathering

Counter-mainia 100 cards, 0 sideboard 1 {Arcanis the Omnipotent} 40 {Island} 40 lands 1 {Callous Oppressor} 1 {Archivist} 1 {Archaeomancer} 1 {Belltower Sphinx} 1 {Callow Jushi} 1 {Consecrated Sphinx} 1 {Jace's Phantasm} 7 creatures 1 {Counterlash} 1 {Tamiyo, the Moon Sage} 1 {Declaration of Naught} 1 {Reminisce} 1 {Put Away} 1 {Psychic Spiral} 1 {Foil} 1 {Dream Fracture} 1 {Fuel for the Cause} 1 {Quest for Ancient Secrets} 1 {Cyclonic Rift} 1 {Jace, Memory Adept} 1 {Mental Misstep} 1 {Vision Charm} 1 {Faerie Trickery} 1 {Dismal Failure} 1 {Scattering Stroke} 1 {Memory Lapse} 1 {Dream Fracture} 1 {Negate} 1 {Exclude} 1 {Bone to Ash} 1 {Jace's Ingenuity} 1 {Lost in the Mist} 1 {Discombobulate} 1 {Geist Snatch} 1 {Howling Mine} 1 {Telemin Performance} 1 {Disrupt} 1 {Traumatize} 1 {Jace's Erasure} 1 {Cryptic Command} 1 {Induce Paranoia} 1 {Lay Bare} 1 {Forbid} 1 {Forced Fruition} 1 {Tunnel Vision} 1 {Convolute} 1 {Dissipate} 1 {Essence Scatter} 1 {Counterspell} 1 {Last Word} 1 {Cancel} 1 {Muddle the Mixture} 1 {Controvert} 1 {Font of Mythos} 1 {Hinder} 1 {Desertion} 1 {Dismiss} 1 {Thought Scour} 1 {Jace Beleren} 1 {Mana Leak} 52 other spells Sideboard

With your goal being to counter as many things as possible, I highly recommend {Ertai, Wizard Adept}.

Draw spells like {Blue Sun's Zenith} are very important too, or you will find yourself out of spells very quickly.

{Kira, Great Glass-Spinner} (commander) + {Arcane Laboratory} + {Erayo, Soratami Ascendant} lockout is possible if you're a hardon. Those cards individually are pretty cool anyway.

 {Force of Will}