Basically there's a Pokemon every generation that gets the designation of "pseudo-legendary", which is iirc not an official term but a widely-used fan one. Generally the criteria for being considered one is being a three-stage evolution line with the final form having a BST of exactly 600. They're typically not common Pokemon either. The idea being that they're legendary-like in their power level and rarity, although not quite on the same level as real Legendary Pokemon, hence the pseudo.
Atm the current pseudo legendaries are Dragonite, Tyranitar, Metagross, Salamence, Garchomp, Hydreigon, Goodra, and Kommo-o.
That's just more reason for me to get it and use it and REK everyone. 😈
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