Ashaya, Soul of the Wild

As long as Ashaya is on the battlefield, it's affected by its second ability and thus its first ability counts itself.

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.

A land that's a Forest has the intrinsic mana ability "{T}: Add {G}."

The ability that defines Ashaya's power and toughness applies in all zones, not just the battlefield.

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).