@BlindTherapy Why would it need to be human? No need for cavern, it's already uncounterable. And it makes FoV, KotR, Teeg, GSZ, Dr. Shaman, Ouphe, etc etc all uncounterable as well. In the right list, you could "almost" get away with zero caverns, letting you run more fetches, wastelands, and a more stable 4-5c list utilizing duals/fetches and Dr. Shamans/Noble Heirarchs.
@serracollector it doesn't need cavern to be uncounterable, but if you are playing 5c humans your manabase has caverns and unclaimed territory that either are set to elf/shaman or set to human. setting one on elf to cast this and having that land function as a colorless source for the rest of the game is a big cost; to the best of my knowledge humans typically play 8 cavern/territory, power, and mana confluence as its initial mana sources, the only non-human creatures being spirit guides or revokers, the latter castable off off-type caverns. playing a fetch/dual/DRS manabase is certainly a good way to play magic but it's going to be a very different deck than 4/5C humans, which is the context in which i replied.
The Value 5C Humans do not run rainbow manabase, that is more a modern format thing. You run highlander dual mana base with plenty of fetchlands. Deathrite is also extremely important (i know it is a non human but my experience tells me Noble is worse at the moment).
I don’t think this card does enough in hatebears. Getting Force of Will’ed is not a big issue for those decks. Getting crushed by your opponents busted draws while you play fair is. This does nothing to slow your opponent, or get you back into the game when you fall behind. If there’s no green combo worth playing in Vintage then this card is a long shot to be playable.
@vaughnbros I think being able to uncounterably cast ouphe is a good stop vs busted. You also get to uncounterably resolve sylvan for CA, channel or Eureka for Emrakul (if you want to be super fun), and other line with good G or GW bears (gaddock, militant, etc.) The main problem is that green doesn't have that many things that are broken on par with the other 4 colors. It's just a notch below red on "broken cards to play," and leagues behind blue.
The routine is Force of Will your first threat, bolt your second, do some cantrips, find either another removal like plow or snap/dread. Then a turn later fetch sanctuary and continue the slaughter. Infinite removal.
That routine needs to be interrupted, it is criminal behavior. I am busting my brains for a while now in finding ways / lines of play but I don't see it. It used to be just snapcaster that represented a double removal on your lovebears. Nowadays they just sweep your board with a combination of counter magic, removal and recurring effects. The plan to "play another threat they can't remove them all" is in my opinion no longer valid. Why would you say that doesn't do anything, it is cheap enough to be played prior to your 'cards that do something'. Shepherd does disrupt, it disrupts their counter magic that is suppose to counter your threats that stop their bombs. Again, it used to be a thing to maximize your disruption by playing only stuff like teeg, thalia, priest, ... and then have all these effects stacked on top of each other to overload opponents, sadly I do not think this approach works anymore, Xerox decks are too strong, they easily dismantle that now.
I am not saying Shepherd is a fix to all this, it should probably have 'hexproof' printed on it as well and then ... maybe (probably still not enough). I do believe the card does deserve at least some testing, we need to find out what 8 'cavern of souls' effects can do.
What is more is that I came to this conclusions 5 years ago and dropped the more redundant and straightforward Human lists. Even back then it was hard (but not impossible) to get a foothold on the game. I started brewing with Human lists that ran all the power and cut on the amount of creatures but still kept enough to do similar 'aggro' things. Dack and Sensei Top enabled deck manipulation (and Dack was also disruption to mana, tinker so it worked well). Tutors got your silver bullets like Karakas, Hurkyl's recall or Decay, or a well timed recall/strip mine. In such a deck I could see Shepherd work. Dack probably needs to go and Oko can take it's place. Top replaced by Sylvan and Ouphe sounds interesting too.