Their whole plan hinges on resolving Stifle to push Phyrexian Dreadnought through, so Meddling Mage naming Stifle can single-handedly strand their combo. Abeyance is excellent both offensively and defensively: cast on your turn it shuts off Stifle, Counterspell, and Foil for a turn, letting your own Replenish or Opalescence resolve clean. Seal of Cleansing has limited targets here, and Intuition is too slow when they can be attacking for 12 as early as turn two, so both come out. Keep your counterspell suite up to protect your own game plan while Meddling Mage locks down their key interaction piece.

Every threat and most of the removal in Mono-Red Sligh is red, so Hydroblast is live against Lightning Bolt, Incinerate, Fireblast, Grim Lavamancer, and their whole creature base. Exalted Angel's 4/5 flying body is very hard for their deck to profitably attack into or race, and the lifegain trigger directly counteracts their burn plan. Intuition is far too slow against a deck trying to kill you by turn five or six, and Mana Leak's tax is easily paid by a deck this low to the ground, so both are cut for more resilient, matchup-specific answers. Prioritize stabilizing the board and racing the damage race with lifegain rather than trying to counter your way through their burn.

Meddling Mage naming Enchantress's Presence, Sterling Grove, or Solitary Confinement rips out a load-bearing piece of their engine before it gets going. Abeyance is strong disruption here too: since it stops activation of non-mana abilities, it can shut off Sterling Grove's tutor ability for a turn, and it denies any instant-speed response while you resolve your own enchantments. Frantic Search and Intuition are both too slow and card-disadvantageous in a matchup that's more about proactively disrupting their engine than digging for answers, so they come out. Seal of Cleansing stays in as your primary way to blow up Sterling Grove or Solitary Confinement once they resolve.