Interesting design space. Not strictly better than forest, because it can (and will) be attacked. That ultimate though, it's probably worth the risk.

Only downside is it being realllly fiddly to drop a counter every turn you want mana. And maybe rules-fixes needed because a loyalty ability at mana ability speed could cause something somewhere to go odd.

There's already more than one planewalker that adds mana to your mana pool. This card can only add mana at sorcery speed.

So you have to float it? Ew.

I mean, vaguely? But again, there are already 2 planeswalkers that add mana to your mana pool.

Also, this design is probably slightly underpowered as is, but it's more of a thought experiment right now.

Also, there would be pressure to make this a "Legendary Planeswalker Land". The Legendary rule is a drawback, even when it doesn't look like it is.

I've seen this pop up a few times, and I haven't been too keen on it. I like this execution. It's simple, yet still Mythic. But I always end up wondering "Why can your opponent attack this land? Why can't it just gain counters, then use the counters?" Using the Planeswalker template is cool, but not playing the cards in your hand because your opponent controls a Grizzly Bears is unfun.

I will say this, though. I think the biggest problem I have with this design is that designers consistantly put the starting loyalty way too low. You shouldn't be able to kill a land with a Shock on the opponent's round 1. My suggestion would be to put the starting loyalty at 4 (and make the second ability cost -8.) +1 for activating the first ability would put this card at 5 before your opponent can respond. They'd need to seriously concentrate on tackling the land either with one big thing, or multiple small things potentially over a few turns. If that happened, then 5-9 damage didn't hit the card's controller, which feels like an acceptable sacrifice for losing a land.

Eh, I like this more as a design:

https://www.reddit.com/r/custommagic/comments/75spbh/genius_loci_a_0_mana_land_planeswalker/

Drawing and other stuff seems unrelated to the card. Note that on the reddit card the ultimate gives an ability to the 'walker itself which is a cute trick as well.

I agree that I do like that design a bit more, but I think both are /slightly/ underpowered still.