For example, Lightning's Swift Strike's innate power of Thundering Destruction used with 5 Fire, 4 Air, and 1 Water can destroy two buildings in the same land, but it cannot destroy two buildings in different lands. Even the final threshold on Serpent Slumbering Beneath the Island's Serpent Rouses in Anger targets a single land, although it affects all lands on the board in addition to the one that it targets.
One sort-of-exception: innate powers that say "Repeat this Power," like A Spread of Rampant Green's innate Creepers Tear into Mortar. When a power is Repeated, you use the power from the beginning, which means you can target a new land.
{1} = You are allowed to pretend you have fewer Elements than you really do — e.g., to activate only the lower level of an innate — but that decision is made for the entire Power, not each threshold individually. Once you've chosen, you must activate every threshold those elements qualify for. Particularly, for Shadows Flicker Like Flames' innate power Darkness Swallows the Unwary, there is no set of elements which can activate the second threshold without also activating the first threshold. If you destroy 2 Explorers to earn fear, you must first gather an explorer (if able).
This can happen, e.g., if the first part of Indomitable Claim reveals an Element on a Presence track, or if the land gets Blighted and the card is Aid from Lesser Spirits.
Likewise if you lose Elements in the middle of resolving the Power, you may lose further thresholds.
For example, if you are playing River Surges in Sunlight, you cannot use water generated by cards played by Ocean's Hungry Grasp.
There are a few power cards that grant elements to other spirits, like Elemental Boon, the innate power Spirits May Yet Dream from Bringer of Dreams and Nightmares, or several of Serpent Slumbering Beneath the Island's powers. Powers with this effect are specifically marked.
Tags: Elements