Is it OK to mention dreams and future plans for a specific company in my SOP when applying for master's degree?
Unlike the other existing answer, I would advise you to tread carefully.


Maybe this is different for a Master's in game development, but generally speaking, "I like to play computer games" qualifies as the #1 worst reason we get to hear about why students are interested in computer science. One of the reasons why this is such a bad motivation is because it shows a certain level of misunderstanding about what computer science is, and I would argue that this is even true for a master in game development.
Even great computer game developers are, to the best of my knowledge, not only interested in gaming, but also in AI, computer graphics and animation, HCI, physical simulation, distributed systems, optimization, etc. Not all of them at the same time, but being "just" interested in building cool games seems rather weak, to be honest. I think it can be pretty much implied that you are interested in games if you apply for game development. Show and discuss your interests in other related areas that sets you apart from all the other applying gamers.
Also, having working at Blizzard as your dream job does not show determination. Many people have this as their dream job, and still do not follow through. Determination is doing something to make your dream a reality despite problematic circumstances, not having a dream in the first place. You should explain what you did, not what you hope to achieve.