Blue has counterspells, black has removal, and red has direct damage and burn, plus the Grixis commander allows a bunch of effects that let you take control of a target creature
Flash is what pushes it over the top for me
Land Path of Ancestry This land enters tapped
Arcades, the Strategist Atla Palani, Nest Tender Daretti, Ingenious Iconoclast Doctor Spectrum Dragon Throne of Tarkir Errant, Street Artist Felothar the Steadfast Invisible Woman Invisible Woman, Sue Storm Opal-Eye, Konda's Yojimbo Pramikon, Sky Rampart Rammas Echor, Ancient Shield Sokrates, Athenian Teacher Super-Skrull Teyo, Geometric Tactician Teyo, the Shieldmage The Fantastic Four The Pride of Hull Clade The Walls of Ba Sing Se
Having to pay 1U extra for any card in the cube makes it worse even if you get a free 2/1 with it
Red Graveyard Hate Reds interaction with graveyards is generally limited