It seems you're tinkering with the deck a lot as it is! :) I have some more "food for thought" for you.

Have you considered the new card, Life's Legacy for your Sideboard instead of Momentous Fall ?

I can see Momentous having more uses, but it's having the 2 cmc instead of 4 that is attractive. to get the same draw for only 2 mana is pretty sweet. Its just too bad it's sorcery speed... and the life gain from Momentous can keep you in the game for longer... but I find that I usually need the cards more and usually at an earlier stage in the game... you're decision of course.

You also have to remember, I need to sacrifice a creature. What creature am I gonna sac turn 2? None since my cheapest creatures cost 3, so the earliest I can sacrifice is turn 4 anyway. Id rather spend the extra mana (which isn't hard to get) and gain some life on top of the draw.

Also what are thoughts on replacing Explore with Yavimaya Elder ? He costs 1 more but I get 2 lands and still a potential card draw.

You have the modern tag/hub thingy and you probably know but Swords to Plowshares , Green Sun's Zenith , and Natural Order are all not usable in modern. Otherwise is pretty sweet +1

I was thinking about Yavimaya Elder for a while, and I think it's a great card and you could do well putting it in but here are my thoughts anyway (keep in mind that I am comparing it to Explore here, not judging the actual inherent worth of Yavimaya Elder because he is amazing!):

I don't like that the two lands go into your hand and not on the BF. Explore and Rampant Growth had got the land on the field making them a legitimate "ramp", while the elder gets them in your hand. Also, there's the potential problem of not having the 2 forests in the beginning that you need to cast the 1GG cost of the Elder, who would give you the forests if only you could cast him. Also, he may be a bit too slow to get the pay-off. I'd be happy to hear counter-arguments but those are just my thoughts right now.

If you are willing to go 3 mana though, I think a better option than the elder might be Krosan Tusker . For one, it goes with your beast theme. I know you only get 1 basic land instead of 2, but you still get the draw from the cycle, and there's always the potential late game to cast him as a 6/5 beast. Plus, you get it from cycling! no casting required, so no counterspells to worry about.

If you want to do a more legitimate "ramp" that puts the cards on the field for 3 mana I would probably go with Cultivate or Kodama's Reach since getting the land is as good as a draw and it gets something on the field for the ramp... or if you want a creature maybe just something like a Wood Elves that gets the land on the field (untapped!)... that's a bit underpowered though.

I do agree that Explore could be replaced though. I love the card, but it is a bit more "situational" than the other options. I think if I wanted to use a creature instead, I would just grab another 2 Sakura-Tribe Elder s. 2 mana, is a creature, gets your ramp, done in one.... but the tusker is also growing in my mind too...

also yes, we all know this is really a legacy deck.

So my thought process, inspired by your Sakura-Tribe Elder suggestion, is to replace my ramp with a creature equivalent. I just like the thought of being able to play a Yavimaya Elder either draw a card and get 2 guaranteed lands in my hand, or hit him with a Natural Order , get a big fatty, and still get 2 lands to my hand. And like Sakura-Tribe Elder , he is a target for Garruk's Horde . I like the cycling creature but for the above reasons hes not as good. But if it comes down to it, replacing Explore with Cultivate is never a bad deal. Cultivate is just aweosme. But I hope you can see why Yavimaya Elder was my first thought. SYNERGY!!!!

yeah, I hear you on making him a target for the Natural Order and Garruk's Horde , and he can get you so many things. I agree that turning those sorcery land grabs into creatures is a good move if its viable since you seem to have mainboarded a lot of the removal in your Sideboard such as Swords to Plowshares and Beast Within . As I said before, I think he's an awesome choice and would do well in that slot. I was just trying to think though all the options carefully and, upon reconsideration, I agree that the Krosan Tusker wouldn't quite work as well... I think I wanted the theme to work too badly there. I'd say try Yavimaya Elder out and see if his 3 cmc gets to be too frustrating because I think, if not for that, he would be the obvious choice.

Yeah it just wound up being that in every game a Swords to Plowshares and/or a beast within is useful. So I think I'm gonna swap in Sakura-Tribe Elder and Yavimaya Elder . well see how it goes, theyre both pretty cheap cards so I'm not breaking the bank by any means.

maybe consider making this deck modern since it is so close already