How do additional land drops work?
Whenever you go to play a land on your turn, the game looks at how many lands you’ve played so far and compares that number to the number of lands you’re allowed to play. As long as you haven’t reached or exceeded the maximum, you’re allowed to play a land.
When you don’t have any effects that allow you to play extra lands, then it’s as simple as checking if any lands have been played this turn, since you’re allowed to play one land each turn because of the game rules. When there are extra land plays allowed, the game looks at your maximum number of land plays at the moment.
For example, you control Azusa, who allows you to play two additional lands on your turn. You play one land, then a second land, and then cast a spell to draw more cards because you’re looking for that third land to play. In response, your opponent kills Azusa. The next time you go to play a land this turn, the game will see that you’ve played 2 lands this turn but can only play 1 land per turn and will deny you that land play. It doesn’t matter that Azusa would have let you play it because she’s no longer on the battlefield and thus her ability is no longer in effect.
