Honestly there's some key things you need to improve on.
1. Your making videos on games that have been out for years, they have millions of videos already made, and people are genuinely already watching better Gary's mod, and superhot videos. I'd try to find a new game to latch on to and make videos on.
2. Your thumbnails don't seem to fit the frame. Half of your "PART1,2... Lettering is cut off.
3. Overall thumbnail design doesn't pop off of the screen. Ask yourself, what will make someone click on this over someone who has 100k subs?
4. I'm on my mobile, so I can't see your keywords. I recommend VIDIQ (chrome extension) to everyone. This allows you to see what other people are using as keywords. It will help you learn.
5. Looks like your being fairly consistent. I'd learn to use a program like Inkscape (it's free). It's like photoshop.
Keep it up brother. Your going to be there in now time. Just keep improving! To answer your question directly. When I hit 200 I started growing about 100 subs a month. Use social media,tell your friends and family
.