Thought Vessel

The Sol Ring you run when you don't need the second mana. A two-cost rock that taps for a single colorless is, by the standards of any ramp shell, a non-event: Mind Stone, Coldsteel Heart, and the rest of the two-mana-rock pile have always been the most fungible inclusion in the deck, interchangeable filler that smooths a curve and asks nothing in return. What lifts this one out of that pile is the rider stapled to the top. Removing your maximum hand size is a static effect that costs nothing to run and matters in exactly the decks that already want a colorless rock: the grindy, card-hungry builds that draw deep and want to keep what they draw rather than ditch the overflow at cleanup. Reliquary Tower and Spellbook do the same job but contribute nothing to your mana; this folds both functions into one slot, which is the entire pitch. The discipline is in the restraint. It does not accelerate you any faster than a baseline two-mana rock would, so the no-maximum-hand-size clause reads as pure upside rather than a power spike that needed paying for. It answers a deckbuilding problem most players don't register until they're pitching their eighth card at end of turn, quietly converting a utility land's worth of value into a ramp piece they were already going to play.