Because it looks like a pseudo-legendary, it has a 600 BST like a pseudo-legendary, and most importantly CAP LC is in the process of getting updated for Gen 8 and it would be awesome to create a new addition for that metagame!
While first stage pseudos are mostly bad in LC because they have garbo BST, some of them have made splashes in the meta before. Dratini was quite viable in Gen 4, and Larvitar wasn't good but was definitely usable in Gen 4 and 5. I think with a proper stat distribution and from the direction movepools are going, we could create a really unique addition to CAP LC.
Personally, this design screams one prevo, in the same vein as Pyroar or Arcanine. However, the stats definitely lean toward the two prevo pseudo-legend route. All I know is that I definitely think this 'mon needs at least one prevo.
As much as I want to picture this as a three stage mon that leads into its BST, I keep coming back to the concept. It feels like to have prevos and keep to concept, we'd probably have to build prevos to fit the Color Change mold we've created. Which means we'd have to do the same with less, which may not be an easy or viable process.
Edit: Having talked it over on Discord, I've been informed that concept usually doesn't apply to prevos. I don't know what we'd do for abilities, but I do love the thought of seeing what kind of mons could lead up to this.
The option for a single prevo does not exist; anyone who tells you is wrong by the law of 600 bst. Realistically we are either getting no evolutions, as it is in line with Mythical Pokemon, or two, as is in line with pseudo-legendaries.
Why I think the former is more effective is simply common trends we see with pseudo-legendaries: They are for almost their entire history Dragon-types or very Dragon-type looking Pokemon a la Tyranitar. The only exception to this rule is Metagross, and for the most part CAP29 does not have any significant similarities to Metagross. In fact, Aurumoth is a much better analog for Metagross, so I think that niche is lost.
Mythical, and therefore no evolution, works much better for CAP29, as it is a rock solid design on its own, and I don't think it needs any sort of addition pre-evolution.
This Pokemon screams mythical Pokémon imo. It has none of the typical Pseudo art trends, and we already made our exception in the form of Aurumoth. This being a full fledged Mythical Pokemon just feels right to me. We never really had one before, so having one would be pretty cool too. Also more previous gonna delay the Prevo Update Process AGAIN. No thanks.
Echoing the general sentiment that this thing looks more like a mythical Pokemon than the final evolution in a pseudo-legend line. G-Luke especially brought up a good point that CAP29's design is jarringly different from any other pseudo, plus its competitive design being more similar to modern mythicals with only having 1 signature/extremely rare ability rather having 2-3 abilities like the pseudos
Definitely feels like more of a mythical than pseudo-legendary. All pseudo legendaries, except for Metagross and Tyranitar, are Dragons, and even then Tyranitar is a draconic/kaiju pokemon. Metagross is the only real exception and that one specifically works since the Champion Steven is a steel type specialist, who wouldn't use Salamence. Leon would never use this mon.
We have yet to do our obligatory two-prevo line and no-prevo lines this generation, so this seems like a perfect opportunity to fulfill at least one of these arbitrary patterns. I think this design better fits the legendary/mythical mold than the psuedo-legendary mold, so I'd say none.
Just because it's not reptilian doesn't mean it can't be a three-stage pseudo (see Metagross). I personally think it gives more of a three-stage vibe like Tyranitar and Hydreigon than a mythical like Zeraora or Heatran.
I think Two prevos makes a lot of sense here; if you look at all of the 600 BST mons in existence you'll note that the only legendary mons that are "big" in that group are Necrozma, The Lati Twins, Genesect, Deoxys, Zeraora, Zarude, Heatran and Landorus-I. Now, the Lati Twin and Landorus-I arent even standalone; they have counterparts (which in lando's case are 580 BST for some weirdass reason). Genesect's a mythical with a large amount of lore and history and Necrozma's has a ton of decently unique lore that justifies its decently unique bst. Realistically, Zarude, Volcanion, Deoxys(who has that weird form change gimmick to justify its lower bst; as each form only needs a singular stat to be superhigh and everything else can go to the dumps), Zeraora, and Heatran are the only standalone legendaries that look bulky and naturally have a 600 BST; which is very little when you consider that the majority of 600BST mons are either psuedos or baby mythicals. You'll actually find that most of these "sub-legendaries" or "standalones" are 580 BST.
Furthermore, most legendaries typically have abstract or natural concepts that they're based on; Necrozma and Deoxys have relations to space and cosmos, Heatran is based on the concept of the core of the earth, Landorus is based on Harvest, etc. Grav's lion is based on a very literal juxtaposition of a painting and a lion's mane, and the entire design revolves around the idea of paint rather than art in general; paint is a very literal and human-made thing. Now obviously there are exceptions to this (the glaring ones being Volcanion and Magearna), but its safe to say that the majority of the legendary concepts are either abstract or nature-based.
I also think that Grav's design fits well with the more caricatured and concept-based Pseudos we've had lately; Goodra, Kommo-o, and Dragapult were all huge departures from the pseudo-legendary norm with their more varied personalities and niche concepts. I dont think its out of the question for Grav's design to be introduced as a pseudo, with GF breaking a lot of their design rules with the recent pseudos. Making it a pseudo would also allow us to make the most out of its design in terms of lore, since mythical pokemon tend to have very supernatural backstories that showcase them as the sole protector of a village or a society or a culture; basically a major hero character. Whereas this design feels much more common and grounded if that makes any sense
Finally, this is really subjective, but I think giving it no prevos would be somewhat of a waste of its design. There's so much in this design that a possible prevo could work off of; the snake, the chimera inspiration, the frame, the cubist aesthetic, the gold; Grav put a ton of soul and inspiration into this design and it would be a shame if the full extent we could explore that through was a Pokedex entry.