The Strategy I figured out was to not shoot any enemies at all, and instead run in circles and extract from any nearby boxes and let said boxes do the enemy destroying. And if the combo does accidentally go up to like 4-6 because of lucky chain box explosions, use like 90 seconds of attacks to defeat the rest of the enemies for insane combos and lots of points (My high score is 48,000 with x11 combo and that's because I just stopped playing. Tell me if you got higher) The strategy makes the game very easy but it is the most fun I've had in this game.
If you're not tired of making this game for the past four days somehow and you decide to expand on it with cooler art and audio and all that stuff, it would be really fun if the playable area was bigger and exploding boxes buffed enemies instead of hurting them, adding lots more fun strategy. Just an idea I had.
Also for anyone who hasn't played this game who is reading this, stay very far away from boxes when they turn really blue and are about to explode. I had to figure that out myself, which failed my first attempt.
Also the hold attack is really satisfying