AND HERE COMES ZACAMA WITH THE STEEL CHAIR
A deck that runs eight* companions. Maybeboard is companion-zone. In spite of the title, there is no hypnosis anywhere in this deck. This is not a prototype, but the site won't let me call a 120 card EDH deck "finished." Also, I definitely made this before the companion rules changed. I am choosing to ignore the errata. I am playing all cards as written.
Companion Stuff:
*As commander, Jegantha's requirement does not need to be followed, so this is not technically the most companiony deck possible. But Jegantha itself meets all seven of the other requirements as well as its own, and is thus one of only two legal commanders for an eight-companion deck. (There are no legal commanders for the even CMC version of this deck. Conversely, there are plenty of legal commanders for a seven-companion deck--by cutting Kaheera you're opened up to all 5c commanders with activated abilities, and by cutting Zirda you can run Morophon.)
Theoretically, a Horde of Notions deck could meet Jegantha's requirement as well as the other seven, but you'd then be restricted to mostly just french vanilla beaters. Seriously, this deck only had like 140 creatures to choose from, and cutting cards like Cavalier of Flame wasn't a step I was willing to take. So, as it stands, I'm positive that this is the most companions an EDH deck can handle while still being fun and "balanced", without more flagrant rulebreaking.
That said, even more theoretically, a deck made up of either all instants or all sorceries (and lands) could also include Lurrus, and still fulfill Kaheera and Zirda's requirements (no nonland permanents is all nonland permanents!) as well as Keruga's. That deck wouldn't have a (legal) commander, but is possible in other casual formats that don't care too much about the rules.
The only possible ten-companion deck would be a deck of all lands. If your playgroup is okay with it, you could even use a legendary land as a commander. If you build this deck...let me know.
Other Stuff:
Speaking of the rules, the one-companion rule isn't the only one I'm breaking. Yorion and Lutri are both illegal companions in EDH, for one thing. The extra 20 lands doesn't hurt too much (manaflooding is less of an issue with multiple guaranteed cards) and Yorion isn't that strong in this deck anyway, so I'm not too worried about him. Lutri, on the other hand, is of course totally banned in commander. However, Lutri is only useful for his ability in ONE instance: if you're copying whatever you copied with Mischievous Quanar. Isn't that great? Because of morph, it'll even be a surprise! (The same is true for Mirrorpool's first ability, so saving your Quanar flip for the right moment might actually change the tide of some games.)
It's very easy and usually inevitable that you'll be able to cast Umori, Zirda, and Lutri all at once the turn after Jegantha comes down, and then Kaheera and anything you have in your hand, and finally Obosh and swing for the win. In one-on-one this might actually be an effective strategy, but even with all the recursion in this deck, firing so many of your seven bullets all at once usually spells disaster in the long term, even if you knock one player out of the game. Besides, everyone else can see that combo too. I'd recommend playing defensively: build up just enough of a board to 1) establish that you're not going for the jugular and 2) deter anyone who tries to target you early. That said, I'd suggest that casting Umori as soon as possible will pretty much always be to your benefit.
There's a fair amount of targeted land destruction, both as a means of interaction and as a way to sac your own Riftstone Portal, which in the late game might give you enough green mana to roll somebody over.
While there aren't a ton of uses for white mana in this deck, getting Emeria to activate is extremely important, so there's a lot of Plains in here. Pumping Windreaver and gaining an outrageous amount of life with Zacama (especially with Zirda out) are your best options for white mana.
Overall, be aware that the landbase is pulling a LOT of weight to make up for only having creatures (of middling quality) in your deck. I'd recommend proxies.
General Thoughts:
For all that it lacks (and all that it has!), the deck ultimately seems pretty balanced, and interesting in its own right. It somehow actually makes sense--Beasts and Elementals with activated abilities are surprisingly compatible, so the deck's subthemes--+1/+1 counters, firebreathing, targeted land destruction--all flow pretty well in and out of each other. Honestly, I think this deck would feel very comfortable as a resilient aggro deck in more forgiving playgroups. (Without lands, it only runs you 85 bucks! Zacama is over a third of the cost!) Eight companions doesn't seem particularly broken here, because in a deck with no mana rocks, one tutor (Tolaria West) and very little straightforward interaction, they provide, not an unfair advantage, but instead the bare minimum of consistency required to make the deck work. Aside from convincing your opponents to scoop out of respect and/or secondhand shame, the defensive aggro game plan is best, with land synergies to keep the engine running. Even though the deck can always blow up around turn 7 or 8, its relative fragility and general rules of politics keep it in check.
That said, believe it or not, the deck is capable of even earlier combo wins, because of the interaction between Marath and, uh, R&D's Secret Lair, provided you have Kaheera (or Incandescent Soulstoke) out. In spite of all my rule breaking, this is the only aspect of the deck that feels potentially "broken" to me. But the lack of tutoring softens the blow, and I refuse to miss out on a chance to abuse such a ridiculous combo. In addition, Quicksilver Elemental can go infinite with Zirda, Hateflayer, and Leyline Prowler, which is also pretty absurd. And that's the whole point, really.
So, finally, I offer the most important advice of all: Be brave. Because when you sit down at the table and reveal the eight dudes in your command zone, you're not starting a game.
You're starting a fight.
