I feel like that may not happen due to it requiring no board manipulation. Destroy 1 gem, row, column, and combinations of those are kind of the game’s form of doing what you just said. It would be nice to see troops that have a mana poll higher than their mana cost to cast.
Color: All 6
Mana Pool: 36
Mana Cost: 18 (if mana is higher than 18, it does not use that mana)
Stats would be similar to that of Fortress Gate, but having much more armor than it does HP and with lower magic than Gate.
Spell: Gives a troop (Magic) mana boosted by unused mana (1:3), give that troop +2 magic, gain an extra turn if 10 or more yellow gems are on the board.
Construct Bond: +2 HP to all construct
Reinforced: +1 armor regen at start of turn
Mana Accumulation: Gains +5 mana at the start of each turn.