I've been going through the exercise of brewing decks that meet the requirements of having certain companions that you can have as part of your "sideboard" so that you have access to casting them from the zone once per game.
I've already done Zirda, the Dawnwaker as a companion along with Kenrith, the Returned King. You can check out the list here => viewtopic.php?f=36&t=24764&p=74556#p74556
Companion
Jegantha, the Wellspring require that you don't have any cards in the deck that have the same mana symbol in the casting cost. This means that you can't have something like Force of Will in the deck as it has as part of the casting cost.
You also can't use the mana it taps for colorless mana of any kind. It has to be on colored mana only.
Commander
The way the deck works is that we are looking to combo win on the turn we cast Jegantha, the Wellspring with the intentions that we already have Sisay, Weatherlight Captain in play.
If you can tap Jegantha, the Wellspring straight away then that means you can activate Sisay. Sisay will have 4 power with Jegantha give two color of mana, so you can search for 3 or less legendary permanent.
There are a lot of ways to give your creatures haste in the deck, so that you don't have to wait another turn to tap the Elk for mana.
Sisay can actually search for a multitude of them, so its better to be patient and search for one of them first before casting Jegantha, the Wellspring.
I've had a Sisay, Weatherlight Captain for awhile now, and posted my list back on MTGSalvation which you can still check out here => https://www.mtgsalvation.com/forums/the ... sts/811613
It has more of a focus on reacting to what opponents are doing, rather than focusing on full combo.
However this meant that I had already spent time working out sequences to win with her.
But I've had to get inventive and find slightly different ways as some of the cards didn't meet the requirements of playing Jegantha, the Wellspring as your companion. Specifically Nicol Bolas, Dragon-God which has triple in the cost.
I'll give you the main example sequences you are looking to do, although it must be noted that there are "backup cards" in the deck in case you've draw them (and don't want to cast) or they have been put into your graveyard or exiled.
This creates an infinite loop.
1.) Cast Sisay, Weatherlight Captain.
2.) Cast Jegantha, the Wellspring and with a haste enabler tap to add .
Sisay, Weatherlight Captain gets +2/+2 with Green and Red colored permanents.
3.) Activate Sisay, Weatherlight Captain searching for Kiora, Behemoth Beckoner.
4.) Kiora, Behemoth Beckoner -1 untaps Jegantha, the Wellspring, then tap to add .
5.) Activate Sisay, Weatherlight Captain searching for Aminatou, the Fateshifter.
6.) Aminatou, the Fateshifter -1 on Kiora, Behemoth Beckoner.
7.) Kiora, Behemoth Beckoner -1 untaps Jegantha, the Wellspring, then tap to add .
8.) Activate Sisay, Weatherlight Captain searching for Oath of Teferi.
9.) Kiora, Behemoth Beckoner -1 untaps Jegantha, the Wellspring, then tap to add .
10.) Aminatou, the Fateshifter -1 on Kiora, Behemoth Beckoner.
11.) Activate Sisay, Weatherlight Captain searching for Teferi, Hero of Dominaria.
12.) Teferi, Hero of Dominaria +1 to draw a card.
13.) Kiora, Behemoth Beckoner -1 untaps Jegantha, the Wellspring, then tap to add .
14.) Teferi, Hero of Dominaria -3 to put Aminatou, the Fateshifter into library.
15.) Activate Sisay, Weatherlight Captain searching for Aminatou, the Fateshifter.
At this stage you use one Aminatou, the Fateshifter activation on Kiora, Behemoth Beckoner and the other on Teferi, Hero of Dominaria.
This means that you can activate Sisay searching for Aminatou, the Fateshifter and another legendary permanent of your choice each loop.
You can literally just keep looping and get infinite mana from lands by targeting them with one activation of Kiora, Behemoth Beckoner, the other activation will still target Jegantha, the Wellspring just so you have the mana to search for Aminatou, the Fateshifter each time.
This means you'll get mana that you can spend on colorless mana, not just Jegantha, the Wellspring mana which can't be spent on generic mana.
16.) Activate Sisay, Weatherlight Captain searching for The Chain Veil, then tap to get additional planeswalker activation's.
17.) Activate Sisay, Weatherlight Captain searching for Ral Zarek.
You can just use an additional Aminatou, the Fateshifter activation on Ral Zarek to get infinite activation's and deal damage to all your opponents with Ral Zarek -2.
If you wanted to you can just cast Jegantha, the Wellspring without a haste enabler and wait a round hoping that opponents don't remove it during their turns.
However the better option is to just use Sisay, Weatherlight Captain instead to get a haste enabler.
There are plenty of these. You can get Hall of the Bandit Lord as a land if Sisay only has 2 power still.
Other options if you do have other cards in play giving Sisay more power are; Chainer, Nightmare Adept, Arlinn Kord, Domri, Chaos Bringer, Sarkhan Vol.
If Jegantha, the Wellspring is killed then you can use Sisay, Weatherlight Captain to search for either Chainer, Nightmare Adept, Kethis, the Hidden Hand, Volrath's Stronghold as a ways to get it back.
There are also backup creatures in Bloom Tender and Faeburrow Elder that as long as you have all five colors in play you can tap for as well, allowing the same combos.
The deck has a lot of fast mana, so your ability to combo on Turn 4 is extremely high.
Decklist
Approximate Total Cost:
Zacama
