https://tappedout.net/mtg-decks/yisan-ultra-budget-50/

Ultra budget constrained Yisan built to adhere to cEDH sensibilities.

Winning the Game
Combo Line
Verse 1: Quirion Ranger

Verse 2: Priest of Titania

Verse 4 (x2): Karametra's Acolyte + Temur Sabertooth

Verse 6 (x2): Great Oak Guardian + Woodland Bellower (ETB finds Prowling Serpopard)

Some things to note:

Ideally on verse 6 when you are trying to double it you'll want to tap lands and Priest of Titania for the required mana. Then with the 2 Yisan activations on the stack resolve the first one to find Woodland Bellower which will find Prowling Serpopard. Then you can resolve the second Yisan activation to find Great Oak Guardian, when it entrs the battlefield its triggered ability to untap everything will go on the stack, then at this point you'll want to tap karametra's acolyte for mana since this is when your devotion to Green will be the highest.
Since Yisan puts creatures into play using his ability once we resolve Yisan we are typically immune to counter magic. However there is one critical time when we are vulnerable to counter magic, that is when we start generating infinite mana since as part of our loop we must recast Great Oak Guardian. It is for this reason that we find Prowling Serpopard with Woodland Bellower, making our combo very difficult to interact with.
Step #1 - Making Infinite Mana:

Assuming no cards in hand, we are tapped out, have no mana in our pool, and the only non-land permanents we have in play are Yisan + the creature we versed for. This means once the untap effect of Great Oak Guardian has resolved we will have an untapped Karametra's Acolyte (11 Devotion to G) Priest of Titania (with 2 elves in play).

Therefore we can simply tap Karametra's Acolyte and Priest of Titania for a combined 13 green mana. Then we can return Great Oak Guardian to our hand using the ability of Temur Sabertooth for 1G and recast it for 5G. His enter the battlefield trigger will untap Karametra's Acolyte and Priest of Titania, meaning we are back where we started having net 5 green mana. We can then repeat this process as many times as we want to generate an arbitrarily large amount of mana.

Step #2 - Drawing the Library:

Now with infinite green mana we have the ability to pull off a lot of shenanigans. To start we are going to use the ability of Temur Sabertooth to return Woodland Bellower to our hand then we will recast it. With its ability we will find Duskwatch Recruiter  . We will then activate the ability of Duskwatch Recruiter  enough times to put every creature from our deck into our hand. From here we will repeatedly cast Acidic Slime (using Temur Sabertooth to return it to hand) to destroy all enchantments, artifacts, and lands our opponents control.

As far as know at this point there are only very select few ways where an opponent could interact with us in a way that results in close to a complete reversal. Here are a few:1. Resolving a suspended Restore Balance2. Exiling Elvish Spirit Guide + Simian Spirit Guide then casting Manamorphose to then cast a Terminus for its miracle cost.

Thankfully we have ways to play around potential outs our opponents might have. So inorder to set up our win to be a sure thing we will next return all our creatures in play to our hand using Temur Sabertooth except itself and Prowling Serpopard. Then we will cast Regal Force repeatedly to draw through our deck 3 cards at a time. We don't want to draw too many cards so as to not risk our opponents forcing us to draw cards on an empty library making us lose after all the work we put in, so we will stop once we have either 5 or 6 cards left in our library.Because some of the cards we want might be stuck in the library we can cast unimportant instants and sorceries then shuffle them into our library using Loaming Shaman then use the same technique with Regal Force to draw until we have 5 or 6 cards in our library again. We can then repeat this process until the only cards in our library are the unimportant instants and sorceries.

Step #3 - Setting up the Win:

Now with infinite mana and our whole library in hand except some cards we don't care about we can go about making sure our opponents wont be able to interact with us when we pass the turn to them. We start by casting Krosan Wayfarer and using his ability to put a land from our hand into play, we then cast Eternal Witness to return him to hand, then return Eternal Witness to hand with Temur Sabertooth so we can put all our lands into play. We will then cast all of our creatures since we need them to not be summoning sick so that we can kill our opponents on our next turn through combat damage. Some of our creatures are also important for denying our opponents the ability to interact with us, the most notable of these is card:Loadstone Golem since its "tax" effect will make it near impossible for our opponents to cast any spells considering they wont have any means to produce mana due to the next cards we put into play. Finally we will cast Root Maze and Titania's Song, these are the final nail in the coffin ensuring our opponents are unable to make mana on their turn.

At this point we can now safely pass the turn. Discarding down to hand size keeping a hand of 7 interactive spells:1. Beast Within2. Nature's Claim3. Natural State4. card:Degalmer5. Unravel the Aether6. Autumn's Veil7. Krosan Grip

Step #4 - Winning the Game:

After passing the turn each of your opponents will get a turn where they wont be able to do anything impactful. Then come your turn you can use the same technique as in step #1 to generate infinite mana and at the same time make all your creatures have infinite power due to the other part of Great Oak Guardian's effect. You should now be clear to attack for infinite damage.

Combat Damage
One of Yisan's greatest strengths comes from the fact that he is an instant speed toolbox of answers. If you find you are forced to spend your early verses answering your opponents instead of advancing your combo, you have the option to find Pathbreaker Ibex as a budget friendly pseudo Craterhoof Behemoth. You have 2 main approaches when going for this plan. Plan A is to find Tendershoot Dryad on your turn so that you maximize the amount of tokens you get, then during the endstep of the player to your right find your Pathbreaker Ibex. The second plan B would be to wait until the endstep of the player to your right and then double your verse 6 and find Woodland Bellower and Pathbreaker Ibex. Depending on your current board state (ie the number of creatures you have in play) the optimal plan between the 2 will change. The main reason you would go with plan B over A is that if you only have weenies in play when finding Pathbreaker Ibex your creatures wont get that big of a buff. if you end up using your verse 3 for interaction and comboing is no longer a viable option consider finding card:Loadstone Golem on verse 4 and going the route of plan A since this will result in the maximum damage.