Eldrazi wants to ramp into Emrakul, the Promised End and Devourer of Destiny while grinding card advantage from Urza's Saga and Kozilek's Command, so disrupting their lands and graveyard beats countermagic. Obsidian Charmaw gets cheaper against their colorless lands (Eldrazi Temple, Ugin's Labyrinth, Urza's Saga), and its enter trigger destroys a nonbasic land, which hits all of those plus Boseiju and Shifting Woodland, while the 4/4 body flies over their ground creatures like Devourer of Destiny. Rest in Peace exiles Malevolent Rumble's milled cards and keeps their graveyard empty, which stops Emrakul from getting cheaper from card types in the graveyard. Containment Priest is a cheap flash body that rounds out the plan. Stubborn Denial and Spell Pierce can only counter noncreature spells, so they can't answer Emrakul or Devourer of Destiny, the threats that matter most. Cut them, plus a Quantum Riddler, for proactive, cheap interaction.

Rakdos Delirium relies heavily on the graveyard for Nethergoyf's power/toughness, escape, and Street Wraith, so Grafdigger's Cage shuts off Nethergoyf's escape cast and any creature recursion from the graveyard. Obsidian Charmaw is a strong flying beater that dodges their ground creatures and removal like Lightning Bolt doesn't kill it outright at 4 toughness. Stubborn Denial and Spell Pierce are too reactive against a deck full of cheap, resilient threats and discard (Thoughtseize) that can strip your hand before you need the counter, so they're cut for proactive graveyard hate. Quantum Riddler is a bit slow against this aggressive matchup, trimmed for more impactful sideboard cards.

Esper Control is loaded with Wraths (Supreme Verdict, Wrath of the Skies), cheap or free interaction (Solitude, Orim's Chant, Silence), and card advantage engines like Teferi, Time Raveler and Narset, Parter of Veils. Consign to Memory comes in to counter Solitude's enters trigger (saving your creature from the exile) and to hit colorless spells like Isochron Scepter. Note that it can't touch Teferi or Narset: Teferi's loyalty abilities are activated abilities, and both are colored spells. Scion of Draco is a clunky top-end that dies to Supreme Verdict, so it comes out. Mystical Dispute is excellent here since it can counter their blue spells (Narset, Jace, Day's Undoing, Teferi, counterspells) for just {U} while still answering anything else for {2}{U}; Stubborn Denial and Spell Pierce are weak since the opponent is happy to play around a tapped-out turn and has plenty of mana to pay through a tax. Wear // Tear swaps in to pick off their Isochron Scepter, filling the extra slot left by trimming Spell Pierce.