Altholz-Troll

If a nontoken permanent that's a copy of Old-Growth Troll dies while it is a creature, it will return to the battlefield as an Aura with both its own normal abilities and the two new abilities granted by old-Growth Troll. The resulting permanent will also retain its name, colors, and supertypes, but it will be an Aura enchantment with no other types or subtypes.

If a token is a copy of Old-Growth Troll, it won’t return from its owner’s graveyard.

If there’s nothing for Old-Growth Troll to legally enchant, it remains in its owner’s graveyard.

If you control but don’t own Old-Growth Troll, you (not its owner) will return it to the battlefield when it dies. You’ll choose which Forest you control it will enchant as it returns to the battlefield.