As a gamer here is what I believe makes a good gaming thumbnail. First I always recommend including the logo for the game you're playing. This draws a lot of attention to people looking for a specific game before they even read the text. Second I am extremely picky about perfection and the text in the blue box is not centered. Also, the boxes themselves are a bit too big, perhaps make them a bit smaller so there isn't so much empty space around the text. And you wanna make sure not to cover the main part of the image, in this case, the PUBg character. And last, the 18 kills text blends a little with the background and thus doesn't entirely stand out. The background has a lot of dark from the shadows and light from the clouds in the sky thus making the black and white colors of the text blend too much. You want that particular text to pop so maybe different colors from the background or an outer glow with a color that pops. That's my thoughts on a thumbnail for a gaming channel.