Most cards can only be played into the active lane and target units in the active lane. Meanwhile, Cross-Lane cards can be played from the active lane into any of the three lanes, effectively making them "global". Cross-lane cards are denoted by the left and right arrows on their mana cost, which are not present on normal, "active lane only" cards. All Improvements are cross-lane cards.
Cross-Lane arrows indicate the card can be played into any lane