Yes, that counts. A tower defense boss that appears every few waves is still a boss, especially if it is clearly stronger, more special, or changes the gameplay compared to regular enemies. So that fits the Boss Battle Edition theme.
And about AI-generated sprites: you can join. Our FAQ says:
“You may use AI tools to assist with coding and asset creation (such as art, music, or sound effects). However, the majority of the code must be your own work, and any AI-generated content should be used thoughtfully and ethically.”
So using AI-generated sprites is allowed, as long as you use them responsibly and make sure they do not copy, resemble, or replicate existing copyrighted content.