How to get Type: Null
Type: Null will be available once you finish the story.
After you clear the story, head to the second floor of Aether Paradise. Gladion will be at the back of the second floor and when you speak to him, you will obtain a Lv.40 Type: Null.
In addition, you will also receive a Memory Disc.
How to evolve Type: Null into Silvally
In order for Type: Null to evolve into Silvally, it needs to be leveled up with a high friendship.
The Memory Disc is an held item exclusive for Type: Null and will change its type depending on the Memory Disc it holds.
Soft-Resetting for a High IV Type: Null
No eggs have been found for Type: Null and the Type: Null’s IV you receive is always more than 3V.
However, if you want to set Type: Null to a specific nature, don’t talk to Gladion immediately after the clearing the story because you must first get a Pokemon with a Synchronize ability.
If a Pokemon with Synchronize is leading the party, any wild Pokemon encountered has a 50% chance of having the same Nature as the Pokemon with this Ability. This applies for Type: Null you can receive from Gladion. Also, the chance of Type: Null having the same nature is 100%.
Timid is the recommended Nature to reset for Type: Null.