I think hippo oath has come a long way since Legends, but there's definitely still improvements to be made.
3 Razor Hippogriff
1 Black Lotus
1 Lotus Petal
3 Gitaxian Probe
1 Increasing Confusion
3 Mental Misstep
1 Nature's Claim
3 Swan Song
2 Burning Wish
4 Life from the Loam
4 Oath of Druids
3 Reito Lantern
1 Battle of Wits
1 Treasure Cruise
1 Aladdin's Lamp
2 Desolate Lighthouse
2 Diamond Valley
4 Forbidden Orchard
4 Misty Rainforest
1 Polluted Delta
3 Tropical Island
1 Volcanic Island
The plan for this deck is pretty evident from a quick glance and I'm sure we've all seen the combo before. We want to oath up Razor Hippogriff asap - none of that non-hippo spirit guide stuff diluting the list - then return Reito Lantern (gaining 2 life) and replace your draw step with Loam to get Diamond Valley out of the yard. Play the Lantern and Valley, then pass.
Your opponent should be pretty worried at this point because of your Hippo, so you can expect them to play defensively and give you a chance to oath up Razor Hippogriff next turn. This time we're getting Aladdin's Lamp if it's in the yard (gaining 10 life) or just sticking with the hippo for value (we don't want to get Lotus - I don't know why you even put that in the list but I kept it for you). We're Loaming up Lighthouse this time and playing it to discard the lamp. Attack with Hippo and sac it to Valley (gaining 3 life) and move it to the bottom of your library with Lantern to avoid decking yourself.
Repeat this until you have so much life that you're out of Tendrils range and mentor would have to deck itself to kill you.
Primary win condition is hippos to the face obviously.
Misstep: obvious inclusion to guard against the inevitable attempt to deck you with ancestral.
Burning Wish: you need this to wish for Channel when you have heaps of life and want to go for the backup plan of Increasing Confusion for lots
Battle of Wits: this is to increase the confusion to make your Increasing Confusion more potent
The optimal sideboard is 1 Channel, 4 Belchers and whatever fast mana you have in your binder.
Rune Scarred Demon is six cents on MTGO right now. Just get that and take out all the bad cards. It's certainly not the best creature, but it's big, it flies, and it tutors. New Emrakul isn't exactly a great target, but it's able to be hard cast and it's only two bucks right now.
@rikter don't be so short-sighted, Rune-Scarred Demon can get ANY Hippo. That's like 4 hippos in one.
That has to be good, right? Hippothetically speaking.
I guess you can't run a non-hippo in the deck, otherwise you'd be a HippoCrite.