My own oppinion and thoughts.
If ya don't like it, downvote the crap out of it :-P
pacifistwestwoman Well, a Boosterset isn't a plane -- But it introduced one:
Kylem. Let's go with that than.
The theme itself fits an sports and arena battle themed plane -- Bullfighting exists.
Only strange if ya look at the content of Battlebond -- There are ony 3 creatures that can take advantage of ya creation:
Here
And therefore ya may never be able to companion ya bull -- In the vacuum of this set alone there is.
i would just add a flavour text to amphasys the struffle of the fighter in the artwork.
But over all -- A solide card imo.
damagicgeek "Companion -- ..."
"As long as ~ is paired with a legendary creature, this creature is a God in addition to its other types gets +X/+X , where X is your devotion to all colores of the paired creature.
Based on "Tyrit" i guess the pane was ment to be
Kaldheim.
A lot of the legendary creatures in Kaldheim are already God's, so that part ot the ablilty may go to waste a lot -- But the inherent synergy with this type is reason enought to implement such a claus imo. -- In a vacuum of the set's speaking.
I would just add a flavour text to explain the role of ya stag in the mythology.
But over all -- A solide card imo.
viriss If ya ment to make a more funny card -- I would use the silver border in this one ;-)
Kaladesh may have some/a lot of vehicles -- But less so cats -- In a vacuum of the set's speaking.
Outside the vacuum -- Most cat's in existence don't have any kind of synergy with artifacts or vehicle's -- The exceptions are
here. So at least I don't know if the whole concept may or may not work out in the end.
BinaryBolas Ravnica --
IzzetNiv-Mizzet lil broodling. Nothing more to say beside that. everything fits imo.
spazlaz ZendikarFit's the style and all -- Not that hard to acomplich with eldrich horror stuff imo ;-)
But what exactly make this one a companion to all the other's that exist? At least for me this could also be no companion and be totaly fine -- And kinda too good cause interaction with emblemes doesn't exist.
bazzboda "Whenever an opponent activates an ability of an non-basicland permanent, ~ deals 1 damage to this player and each planeswalker he or she controls."
Whatever plane that is supposed to be :-)
I don't like the "or". Companions should have one, and only one, destinced way of limit ya in dech building.
bastardneko Based on the artwork -- If ya ment to make a funny card -- I would use the silver border in this one ;-)
"... contains exactly one legendary creature ..."
Whatever plane that is supposed to be :-)
Limiting yaself to only one other creature on the board seems kinda harsh -- I would just change that to legendary creature.
ganzzert Fiora -- Would have never been able to figure that out tbh :-)
Your little story of bullying other pet's doesn't resonate in the slightest with the card itself imo -- Besides the "still being kinda liked" (shroud).
It feels more like a vandalistic approach than a bully one (Throwing scrumbles around to smash other stuff in -- therefore the owners removed all the scrapp that he could throw around) -- And that is something a "real" dog can't realy do ;-)
ZephyrPhantom Arcavios -- At least i believe that is what that is supposed to be.
Haste seems kinda unnessessary -- Cause most of the time ya have him/it on the board log before ya trigger threshhold (i know it isn't threshhold -- be the closest remnence to that)
But, well, Strixhaven is a school of magic and stuff -- Therefore it feels kinda stange to build a deck without "real magic" in it.
Vunik "... ~ deals 1 damage to any target and you gain 1 life."
Whatever plane that is supposed to be :-)
I realy don't get the terror feeling ya name implies. The artwork is kinda too cute for that.
sdfkjgh Lorwyn-ShadowmoorApperently a sublement to Doran, but... Ya card does far more than Doran ever does. It feels more like Doran is the companion of ya card than vice versa.
Jartis Alara
And no it wasn't as obvious as ya might thought -- Cause Esper used hybrid mana in not a lot of creature/artifact cards there were
1,
2,
3 that I could think of ;-) Therfore ya might edit the mana cost to make it more obvious.
Beside that -- A Borg - Worm (Assimilate them all) fits kinda nicely.
foureyesisafish Whatever plane that is supposed to be -- Maybe Lorwyn cause of the
Boggart's, but they are goblins. So I realy don't know.
Omnath may have the static version of ya mana ability -- But I realy don't know if ya being able to indeffinetly keep ya generated mana without such a measure -- if ya take in comparrison that all other effect that preserve unspent mana only work until end of turn:
Here
hydraheadhunter Whatever plane that is supposed to be :-)
Everything ya cast is a spell -- ya may just reword it to "Add one mana of any color. Use this mana only to cast spells." But that would counteract with ya 2nd ability, so i get the strange wording.
"Then, if..."
The whole card may make more sense to me if i could figure out the plane :-)
zybourne Innistrad
"Whenever you gain life for the first time each turn, create a Blood Token." --
herePretty simplistic -- And that is never a bad thing.
inverness Kamigawa -- And i appriciate ya laugther for propper clarification of the plane's -- lol
Short and planely -- cause ya card is also short and simple: It doesn't work at all.
Companion checks the content of ya deck, it doesn't alter the rules. Therefore ya won't be able to cast it as an companion.
vizionarius Lorwyn -- ShadowmoorYa avoided nicely the cmc 1 everywere problem ;-)
I guess ya still could reduce the cost of the ability to cmc2 -- Cause the bord state is something that can be easaly be dealt with.
the5lacker Whatever plane that is supposed to be :-)
Looks more like a horro than a knight tbh.
And I don't get the feeling of a companion -- More like a stand alone ruler -- Cause he does faar too much.
any time you could cast a sorcery.)
Or if the card could only be legal in singelton formats..
"When in doubt, do a common." 
Will try to get things moving later on today. 
is very strong.