Some more steps towards paying mana costs according to the rules.
It is quite a challenge to add this feature as it was built around its own mana cost system to have the better AI.
Player started with 4 Mountains in play. A
Gut Shot is played and the choice is made to pay 2 life. Then a
Mountain is played.
The
Moltensteel Dragon is played. The player is asked to either pay 4 red mana and 4 life or 5 red mana and 2 life which are the only possibilities. The player taps 3 Mountains for mana.
Two more Mountains are tapped and the
Moltensteel Dragon is on the stack with the player selecting 5 mana and 2 life as cost.
Another
Gut Shot is played. This time the only choice is 2 life so the spell can go directly on the stack.
In the messages on the right the details about the payed costs are shown.