This is a great take on the vampire survivors formula! The flag mechanic opens up a lot of options, especially when it comes to maneuvering the minions without placing the flag. For example, since the minions are faster that the player, I found myself quickly sending them to free other minions, or moving them behind the character to bodyblock bullets. One quality of life improvement that I would like is being able to recall the flag before placing it with right click. I also think some way to aim the minions while the flag has not been placed would (maybe they could shoot in the direction of the closest enemy). I don't think I played the game was intended way, but I enjoyed it a lot!
PS: I did kill the frog, but it was a pain because other enemies where always on the way, stopping me from getting close. Once I isolated him, he died fast enough. Despawning enemies when the boss spawns would solve that problem, and also put the player's attention on the boss. The big enemies are a bit too bullet spongy.