Bland Pokémon are a special type of Pokémon introduced in Generation VI and a key mechanic in Pokeland. They consist of Pokémon from the past who have yet to develop a type. It is similar to the Normal type, but also quite different, with many differences from other Pokémon types.
When a Pokemon is bland, it will have Normal as it's primary type and Bland as it's secondary. Bland Pokemon are unable to have STAB from attacks. The Bland type cannot be had by any Pokemon that is not Bland (so a Porygon, for example, could not Converge into Blandness), but most Pokemon from the past are bland. All attacks known by the Pokemon are Bland types, which act like Normal types and change back to their first typing when Sketched or when the Pokemon's type is returned. When Ditto transform into the Pokemon they will have regular typing on the Pokemon and attacks.
Sometime around when the Pokemon World was just created, very few Pokemon had types. As such, when Ronald and Sara traveled back in time during Pokeland, all their Pokemon and the ones they met lost their typing. In order to get their typing back and typing new ones, they had to fulfill their Typing Requirement or TR for short. Because the Time Trainers' Pokedex were synced with the HQ's server, when they we nt back in time they had to start fresh, and because some types didn't have any Pokemon they had to type some and get the info on it. Once they found all the types, the Pokedex was updated and was able to repower the Time Traveler.
Some Pokemon can only learn new moves after getting their types back, so it would be advantageus to send Pokemon from the Pokemon PLAY or other Generation VI games to remove their typing and bring it back so they learn better moves, along with leveling up or even evolving.
Fire: Dip in lava or bring into some hot area.
Water: Bring into water.
Grass: Give and speecial berry or bring to forest.
Electric/Flying: Bring them to a cloudy area.
Ground: Have them use Bland Dig or bring them into Quick Sand.
Most Pokemon: Hit them with an attack that is typed their base type is.