Ashaya's power and toughness are each equal to the number of lands you control. Nontoken creatures you control are Forest lands in addition to their other types.
2020-09-25
A land that's a Forest has the intrinsic mana ability "{T}: Add {G}."
2020-09-25
As long as Ashaya is on the battlefield, it's affected by its second ability and thus its first ability counts itself.
2020-09-25
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to Ashaya may become lethal if lands you control leave the battlefield during that turn.
2020-09-25
The ability that defines Ashaya's power and toughness applies in all zones, not just the battlefield.
2020-09-25
You can't play creature cards as lands; you'll still have to cast them as spells, and they'll enter the battlefield as lands (in addition to their other types).