Confidence:StrongSolidPlausibleTentativeSpeculative

• Painter's Servant✓

  2

  Artifact Creature — ScarecrowC

  Alternate win condition: one card wins on a state the other reliably produces (empty library, infinite life, etc.).
• Intellectual Offering

  4U

  InstantU

  Intellectual Offering untaps all (or many) permanents, refreshing Grindstone's tap activation.
• Unstoppable Plan

  2U

  EnchantmentU

  Unstoppable Plan untaps all (or many) permanents, refreshing Grindstone's tap activation.
• Seedborn Muse

  3GG

  Creature — SpiritG

  Seedborn Muse untaps all (or many) permanents, refreshing Grindstone's tap activation.
• Unwinding Clock

  4

  ArtifactC

  Unwinding Clock untaps all (or many) permanents, refreshing Grindstone's tap activation.
• Paradox Engine

  5

  Legendary ArtifactC

  Paradox Engine untaps all (or many) permanents, refreshing Grindstone's tap activation.
• Dramatic Reversal

  1U

  InstantU

  Dramatic Reversal untaps all (or many) permanents, refreshing Grindstone's tap activation.
• Blinkmoth Infusion

  12UU

  InstantU

  Blinkmoth Infusion untaps all (or many) permanents, refreshing Grindstone's tap activation.
• Shifting Woodland

  LandG

  Graveyard copier: one card stocks the graveyard (mill, surveil, dredge) and the other can repeatedly become a copy of a card that's there, borrowing its abilities without recasting it — the Shifting Woodland + Aftermath Analyst shape.
• Rings of Brighthearth

  3

  ArtifactC

  Grindstone has activated abilities that aren't mana abilities, fueling Rings of Brighthearth's activation-trigger.
• Kurkesh, Onakke Ancient

  2RR

  Legendary Creature — Ogre SpiritR

  Grindstone has activated abilities that aren't mana abilities, fueling Kurkesh, Onakke Ancient's activation-trigger.