One little gameplay tip for you: always look for opportunities to create 4-matches and 5-matches to generate extra mana and extra turns. There are certain patterns that allow you to collect a 3-match and then have a 4-match fall into place. For example, at 27:57 of your stream, if you match the three yellow at the bottom of the screen, the two yellows on the 4th row from the bottom would fall beside the two yellows on the 3rd row from the bottom. I know your team doesn’t collect yellow, but this is just one example. Extending your turn and taking more mana is never a bad thing.
A similar idea at 29:39: if you make the vertical yellow 3-match by moving the yellow gem 3rd from the left and 4th from the bottom, you would allow the skull in the 2nd row from the top to drop in beside the two in the 4th row from the bottom. You’ll see that the AI took that move at 30:13 to kill your Nyx. The AI doesn’t actually think ahead that way (it just got lucky), but there are lots of little opportunities that you can learn to recognize the more that you play.
You are already doing a good job in denying the AI its mana by thinking about what colors it uses and keeping them away from it - that’s pretty advanced play for a level 18!