Semi-Pseudo is a term used to describe a Pokémon who is often mistaken for a pseudo-Legendary, but fail to meet the criteria to be a pseudo-legendary. The most notable example of this lies in the fact that all the semi-pseudos have a base stat total that does not equal 600, so they cannot be considered pseudo-legendary by definition. Pseudo-legendary Pokémon are usually uncommon/rare.
Hoenn is the only region, as of yet, to contain 2 Pseudo-Legendary Pokémon instead of just 1.
Coincidentally, they are usually found in hard-to-find places. For example: Bagon (Salamence's basic stage) can only be found at the back of Meteor Falls Cave with the use of Surf and Waterfall, meaning that you'd need eight Gym Badges to even think about going there and Metagross can only be obtained after the player defeats the Elite Four and Steven, the player must then go to Steven's house, the player then receives a Beldum.
Flygon, a Semi-Pseudo Legendary, is also found in Hoenn.
Lucario and Zoroark are mistaken as Pseudo-Legendaries because of the way in which they are to be obtained.
A Lucario can also be obtained in Pokémon X and Y at the Tower of Mastery after you beat the Shalour City Gym leader, Korinna and have obtained the Key Stone. You'll be instantly challenged to a Mega Lucario VS Mega Lucario battle against Korrina.
Zoroark was once only able to be caught as an event. Because of this, it is mistaken as a Legendary. Zoroark could be obtained when either the event Raikou, Entei or Suicune was taken to Lostlorn Forest outside Nimbasa City in the first Black & White. It was also possible to obtain Zoroark's pre-evolution, Zorua, but Zorua needed an event Celebi to be captured in Black & White. However in Black & White 2 the player is given a Zorua by the sage in Driftveil City provided they have room in their party for it to fit, it seems that it was once belonged to N. In Generation VI player characters in the Pokémon Village or on Route 20 have a low chance of running into a wild Zoroark.
Tyranitar and Metagross are the only Pseudos that cannot learn Dragon-type moves by leveling up.
However, Metagross is the only Pseudo-Legendary that cannot learn a Dragon-type move at all.
All Pseudo-Legendary have been used in a battle with a champion at one time or another: Lance has a Dragonite in Gold/Silver. Blue (Blue/Green) has a Tyranitar in the rematch in FireRed/LeafGreen. Steven has a Metagross. Lance has a Salamance in the Pokémon Black and White 2 world tournament. Cynthia has a Garchomp. Iris had a Hydreigon and Diantha has a Goodra.
Every Pseudo-Legendary, at level 100, have a total experience of 1,250,000.
Goodra is the only Psuedo-Legendary with one type.
Most Pseudo-legendaries have a 4x weakness except Goodra and Metagross.
Out of the seven Pseudos, four of them can mega evolve, while two out of the nine Semi-Pseudos can.