I chose Mirri to be my Voltron. She's fast, evasive, and fights other creatures well. This list is meant for dueling, but it can perform well in multiplayer (if you don't play too suicidally). The goal is to blast your opponent's hand as quickly as possible, control the board with targeted and mass removal, and then when the coast is clear, beat in with Hatred and/or Lashwrithe/Nightmare Lash/Strata Scythe/Blackblade Reforged/Liliana of the Dark Realms. Mirri is fairly cheap to recast, but if things drag on and spells become too expensive, Extraplanar Lens, Gauntlet of Power, and Caged Sun are there to help.
1 Mirri the Cursed
Sorcery (23):
1 All Is Dust
1 Beseech the Queen
1 Brainspoil
1 Bubbling Muck
1 Damnation
1 Dark Petition
1 Dead of Winter
1 Demonic Tutor
1 Diabolic Tutor
1 Dimir Machinations
1 Divest
1 Duress
1 Hymn to Tourach
1 Languish
1 Mind Shatter
1 Mind Sludge
1 Mind Twist
1 Mutilate
1 Never // Return
1 Praetor's Grasp
1 Read the Bones
1 Sadistic Sacrament
1 Thoughtseize
1 Defile
1 Devour Flesh
1 Diabolic Edict
1 Dismember
1 Go for the Throat
1 Hatred
1 Hero's Downfall
1 Imp's Mischief
1 Liliana's Triumph
1 Murder
1 Shred Memory
1 Silence the Believers
1 Skeletal Scrying
1 Sudden Death
1 Snuff Out
1 Withering Boon
Enchantment (3):
1 Necropotence
1 Phyrexian Arena
1 Tainted Aether
Artifact (14):
1 Blackblade Reforged
1 Caged Sun
1 Champion's Helm
1 Darksteel Plate
1 Extraplanar Lens
1 Gauntlet of Power
1 Inquisitor's Flail
1 Jet Medallion
1 Lashwrithe
1 Loxodon Warhammer
1 Nightmare Lash
1 Oblivion Stone
1 Perilous Vault
1 Strata Scythe
1 Karn Liberated
1 Liliana of the Dark Realms
1 Liliana of the Veil
1 Liliana Vess
1 Ugin, the Ineffable
1 Ugin, the Spirit Dragon
Land (37):
37 Snow-Covered Swamp
Multiplayer Substitutions:
1 Thoughtseize
1 Duress
1 Divest
1 Hymn to Tourach
1 Mind Twist
1 Mind Shatter
1 Mind Sludge
1 Sadistic Sacrament
1 Tainted Aether
1 Sol Ring
1 Commander's Sphere
1 Darksteel Ingot
1 Wayfarer's Bauble
1 Sensei's Divining Top
1 Torment of Hailfire
1 Exsanguinate
1 Decree of Pain
1 Masterwork of Ingenuity
Horde of Notions | Azami, Lady of Scrolls | Mirri the Cursed | Kaalia of the Vast | Ghave, Guru of Spores | Nin, the Pain Artist | Damia, Sage of Stone | Derevi, Empyrial Tactician | Vela the Night-Clad | Jhoira, Weatherlight Captain | Nahiri, the Lithomancer | Princess Twilight Sparkle