First off, I would say that you need to hire someone to create a banner for you and create some thumbnails templates that you can alter for other games. You can find people that will do this for $5 on Fiverr or even cheaper on Twitter. I'm not saying what is there now isn't satisfactory, it's just your channel needs a bit of work on the marketing aspect.
Also, to expand your channel, I would most certainly advise that you need to utilize social media platforms. Just utilizing them alone, I've been able to receive just about ALL of the subscribers I currently have. I have never completed the Sub4Sub transaction, and I recommend you do not either. It's very easy to be seduced to gain a subscriber count that way, but in the longer run it will destroy the channel and deter the audience away.
Also, I would like to advise that this is not the correct location to advertise your channel. If you read the stickied post, the administrator states not to advertise as the first bulletin point:
Things you should not do in the discussion sections:
- No advertising Links (No links to your own channel, videos or social media.)
I'm just trying to look out for you and not get you banned! Good luck with your channel! You certainly have potential.