I know I covered this before, but I can recap again. All pseudos, even Tyranitar and Metagross, the only non-Dragon ones, have a distinct pattern; 3 stages, 600 BST, and 1,250,000 XP at Level 100, because all of them follow the Slow level up chart. They all also have a tendency to evolve very late (Metagross at Level 45, and Hydreigon at Level 64 are the extremes.)
The Pokemon that follow this exact pattern are; Dragonite, Tyranitar, Salamence, Metagross, Garchomp, Hydreigon, and Goodra.
Pseudo-Legendary is technically a fan term. It got the prevalence it does because of this pattern. You know how there's a regional Pikachu in every Gen? This is about the same as a 'regional Dragonite.' However, they're not all Dragon, and they are extremely powerful (The common legendaries have 580 BST, The Mythicals have 600, same as them, and Cover Legendaries have 680.)
Pseudo-Legendary means Fake Legendary. Dragonite was obviously meant to be something, given the attention he gets in Kanto and Johto. They are always fought near the end game, usually with the Elite Four or Champion. But they're still not actually legendaries by any of the other definitions that has. The name reflects both of these things.
Arceus lies outside even other Legendaries, and Mythicals, though. With 720. It gives him 120 in every stat. And that's where my own idea for Silvally comes in. He could be like Arcanine and Volcarona - extremely powerful, more than the starters, but less than Legendaries. (Starters have 525-535, Arcanine and Volcarona have 555 and 550 respectively.)
Due to the idea of him having an equal spread, he could actually work with as low as say, 540. Same as Haxorus and Snorlax.
This would give him 90 in every stat. That's decent, and with his ability to become any Type, he could make good use of it. That's speculation now - obviously the BSTs weren't there to mine. The actual game's gonna have to have it done to learn it.
