Double Vision is a YouTube game of Happy Tree Friends. The game is similar to "spot the difference" games, where the player has to spot the difference between two images. The game has a time limit, however, seeing as it is a YouTube video, it can be paused for unlimited time to complete the game. When a level is complete, a short death scene from a Happy Tree Friends episode plays as a reward before moving on to the next level.
Truffles in Level 11 of Double Vision.
There were originally six levels of Double Vision. However, due to popular request, new levels were recently added, giving the game 12 levels. There is a chance that more levels will be added in the future.
Here can be the link to the game: Double Vision on YouTube