Implementing billboarding, camera position checks and forward checks to select a suitable sprite from a given tilesheet/spritesheet/spritemap. This enables us to only use quads and avoid manipulating the sprites through script, which should increase performance for scenes with plenty of background characters.
Implementing both billboarding and scrolling the tileset/tilemap of the character to update the face being displayed according to the camera's position
Learn How to Import a Tilemap/Tileset to Create a 2D Platformer Game Level in Unity