Sure! Here's an example of how the game could be implemented as a single HTML file using JavaScript:
In this implementation, the Kart Kid ("blue" rectangle) acts as the tower and can summon Kart Kids as enemies. The Kart Kid's health scales with its level, and at Level 5, it becomes invincible for a short amount of time and deals damage to all enemies it passes. The enemies ("red" rectangles) come in waves, and as the waves progress, they become stronger. The final boss appears at wave 25. The game is designed for smartphone operation and uses canvas for rendering the game graphics.