"Pseudo-Legendary" is a fan-given name to Pokémon who have stats similar to a Legendary's, but are not actually Legendaries due to the fact that they evolve.
Low Tier Legendaries are Legendaries that have lower stats than an average Legendary, and are usually easier to find.
Some Low-Tier Legendaries include: The Legendary Bird Trio, (Moltres, Articuno, Zapdos) the Lake Guardian Trio (Mesprit, Uxie, Azelf) and the Forces of Nature Trio. (Tornadus, Thundurus, Landorus)
Mid-Tier Legendaries is an average Legendary Pokémon, and are good enough to defeat the Elite Four.
Some Mid-Tier Legendaries include: Deoxys, the Legendary Beast Trio, (Entei, Suicune, Raikou) the Regi Trio, (Regirock, Regice, Registeel) the Tower Duo (Ho-Oh, Lugia),Manaphy, Cresselia, Shaymin, Meloetta and Mew
High Tier Legendaries are Legendaries that are generally rarer and have higher stats than an average Legendary Pokémon.
Some High Tier Legendaries include: Mewtwo, Darkrai, the Creation Trio, (Palkia, Dialga, Giratina), Jirachi, Victini, the Tao Legendary Trio, (Reshiram, Zekrom, Kyurem) and the Weather Trio, (Rayquaza, Kyogre, Groudon), Heatran, Eon Duo, (Latios, Latias), the Swords of Justice( Keldeo, Terrakion, Cobalion, Virizon,), Genesect, and Regigigas
There is only one Special Legendary in Project: Pokémon. However, this Pokémon is only available to admins, but could possibly be released to the public any time. The Special Legendary is Arceus.