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I don't know what you did wrong without taking a peek at your project. However keep in mind that tilengine is a graphics engine to program video game graphics with it, it doesn't provide any ready-made assets collection, only the assets used by the examples themselves. There isn't any sonic sprite pack, you have to build your own.

can't i just download the sprite pack from pictures?

A sprite pack is usually comprised of two files: a single graphic file containing many related pictures together, and a text file describing where are located every picture. Just downloading a single large pack is not enough, rectangle coordinates for each sub-picture are required.