Dimir Midrange is loaded with cheap, efficient interaction (Thoughtseize, Fatal Push, Counterspell, Force of Negation, Spell Snare) and card advantage engines like Orcish Bowmasters and Psychic Frog, so we want threats that dodge their removal suite and equipment that's cheap to reload with. Slippery Bogle is hexproof, completely immune to Fatal Push, Thoughtseize can still strip it pre-cast, and their removal spells, letting it carry an equipment through their disruption. Stubborn Denial is a cheap way to protect our key spells from Counterspell or Force of Negation once we have a big creature online. We trim slower or more easily disrupted mainboard pieces for resilient threats.