Automatic X on cards with X cost

[fabiorlopes]

When casting a X cost card or activating a X cost ability, the game could see if you have mana in your pool and suggest that ammount for X.
For example, activating Lair of the Hydra with 8 mana on the pool should suggest X=7 (since Lair ability is XG)

 

[ManaDrainThis]

That would be a nice little improvement.