Really cool auto-battler! I had fun experimenting with the mechanic and learning it. I like the potential of the combining mechanic.
It was cool getting a front-line sweeper with a high attack. It did end up feeling a bit cheap that a high attack unit wouldn't take any damage. After the 1st couple waves, the game is pretty much won. But there's lots of opportunities for different challenges.
I think it'd be cool to hover over the purchased units to see unique combination names and with how many more combinations they have left.
Nice job!