Ein schönes Video hierzu nochmal: https://www.youtube.com/watch?v=4F3OF8cjsAA (kanntet ihr das schon?)

People think the scene is completely practical but not really XD
It's a fusion of:
- mostly practical (before when his hair starts to grow, and after the transformation and the base)
- stop motion (frames and clips rapidly move after eachother)
- CGI (final touch, morphing the frames more effectively, especially during the decomposing part of the transformation)

CGI is not bad. If used well it's absolutely gorgeous to look. Heck, Jurassic Park did it and that was back in the 90's. The trick is that if you want to create something believable you have to use several forms of effects to fool the audience easier, like they did here! And almost no movie does that anymore, CGI has dominated the industrie completely.

Jurassic Park used a different effect for each scene, heck each moment in a scene. Every now and then an animatronic is there, then the CGI model kicks in, and back to the animatronic. If you vary with effect forms it is harder for the audience to tell which is which and is easier fooled.