Circle of Protection: Red is strong against a deck whose entire plan is direct damage and red creatures, since it can repeatedly prevent damage from any single red source each turn, including burn spells and attackers. Phyrexian Furnace is irrelevant since Sligh has no graveyard synergies worth disrupting, so cut it for the Circles. Keep Swords to Plowshares as premium removal against Ball Lightning and Grim Lavamancer, and Wrath of God to reset the board against a swarm of small red creatures. Standstill is risky here since Sligh wants to keep casting cheap spells anyway, so be judicious about when you commit it.