Forestation 2G
Enchantment
All nonbasic lands are forests.

Green is the weakest color in eternal formats by far. Yes it has big creatures but it has minimal interactions and few ways to hate on opposing strategies. A card like this would instantly make Green Stompy a viable option, and would make monogreen a viable color in the format.

Hating on nonbasic lands is very green. Green is all about nature, green nonbasic land destruction has been a part of MTG for a long time.

Eternal formats would benefit from being more friendly to monocolored strategies, especially green based monocolored strategies (lots of players love beating down with creatures). Every other color has viable monocolored strategies (Mono Black Reanimator is actually quite powerful), but in green, even Elves have to splash black to have any chance of being competitive.

Manabases in eternal formats are obscenely expensive and create a high barrier of entry for new players. The format making room for more monocolored creature friendly strategies is essential to the longterm health of legacy.