How do you get dementor on Lego Harry Potter Years 1 4?

You can't actually get a Dementor as a playable character in Lego Harry Potter: Years 1-4.

However, you can encounter them in specific levels throughout the game, such as:

* Hogwarts: Year 3, Level 1 "The Dementors"

* Privet Drive: Year 4, Level 2 "The Dementor's Kiss"

In these levels, you will face the Dementors as enemies and have to defeat them using various spells and strategies. You can also find Dementor minifigures in some of the game's sets.

Remember, Dementors are not playable characters in this version of the game.