"Mana Block" select a certain mana color that your troop will not collect for (100 gems)(or whatever resource). it would stay blocked until you buy that color back for the same price it cost to block.
say like my team
* Stormhammer (blue/brown/yellow)
* Ragnagord (red/brown)
* Dragon Soul (red/purple)
* Famine (green/yellow/brown)
I would bock brown mana for Stormhammer in order to help Ragnagord's mana collection