Have you ever tried forums. I know that there are a lot of gaming forums out there. Be active in those forums and then show your video's. Yttalk is a forum also.
Also collaborating is a great way to get more exposure. You can try to collaborate with some big youtubers. Watch their video's and comment like and share them. They will then more likely wanting to help you. Besides that you can also collaborate with smaller youtubers. Not just by making videos with each other, but also by sharing each others video's and reccomend each other's channels. It works so much better to grow with each other then to grow alone.
The one that works the best for me is ranking in youtube search. For each video, I take a look at what keywords I can use to get them ranked for. For instance, I had a tutorial about animating fire in Anime Studio. So I looked up ''How to animate fire''. Youtube then gives the suggestion ''How to animate fire'' when you type it in, which means it is searched for a lot. I also looked for ''Anime Studio fire'' and it also give it as title suggestion. I noticed that both keywords didn't have much videos with those keywords in the titles when you searched for it, and those who did, didn't have many views, which means it is easier to rank for. So then I put as title ''How to animate fire in anime studio'' and I put the same words in my description and tags. It is now ranked for both keywords. If you would try to do that for all of your videos, soon you have a bunch of videos ranked in youtube search, which will give you a lot of viewers and hopefully subs.
Those are the things that I do to get subs, and I definitly noticed some growth.