I can't say I like any of the aforementioned ideas aside from a couple of SGs.
Dimensional Gate. Gate between two different dimensions. Can be used for free long distance fast travel. Also members of the posseessing element can return to this gate anytime from anywhere for free.
Floating Fortress. Attacking decks must use air creatures. Allows all members of the possessing element to retreat successfully regardless of opponent's stance. Allows members to retreat without using an action points.
The Black Mist, possessing element gets a new action ability. They gain the ability to conceal themselves in an impenetrable black mist which makes them completely untargetable for three turns while they are still able to attack and move freely.
The Gates of Hell. When the members of the possessing Element are slain, rather then forced to wait the required number of turns before respawn, they are automatically respawned here.
The Unending Caverns. Possessing element can fast travel to any connected hexagon controlled by their element instantly and they can do it from any connected hexagon under their element's control. And by connected I mean there should be a line f controlled hexegons from point A to Point B.
Chaos Orb. Huge mysterious orb hovering above the ground. Touching it causes a random, but usually beneficial effect.
Lake of Fire. This cheap source of heat fuels the fires of thousands of smiths, the possessing element gets its resources doubled.
Gravity Pool, an area of impossibly strong gravity. He who walks through it can scarcely stand. But its powers can be manipulated and its powers have been manipulated. The possessors can use this source of gravity to make all of their equipment very heavy to bear for those whom it doth not belong to. Meaning when one loses a battle, instead of six cards lost, the enemy can only carry the weight of four.
Tree of Life. The vitality and stamina of this tree gives to to those who partake of this fruit means the possessors can live longer in battle. Taking of the tree's fruit provides a one time action ability, revitalize. Revitalize when used means that lets say they lose their 2 out of 3 match, they can choose to use revitalize to give themselves another chance. Basically turning the match from from a 2 our of three to a three out of four (For their enemies) and a 2 out of 4 (for themselves). Once used they must travel back to the tree of life for another fruit.
Palace of Light. Its a palace constructed of light made still. This is the only one that does create creatures, it creates light creatures, one per turn allowing the possessors to take as many of them as they need. However they must be actually inside the palace to gain these creatures.
Temporal Mirror. Its a magic mirror that tells the future. Looking into it provides the one time Action ability"Precognition" Precognition allows one to look at their opponent's deck before the fight.
The wishing well. Allows people to come and make a wish, granting the action "Wish". Using the action "Wish" will allow them to either construct a deck made up of any unupgraded cards that they wish to use for one battle, or it will allow them to temporarily upgrade six cards for one battle.