Finally got the hard badge. It was very difficult and took many many attempts, and restarts from checkpoints. From start to finish you cannot waste points.
BUG with the bestiary badge - I completed the bestiary by killing the last boss, but it did not register the badge. My bestiary is full, i had found the 2 hidden guys on my own. Maybe the badge works for normal kills filling the bestiary, but my first time beating the game filled it for me, and no badge. (no connection issues, other badges registered)
To the people asking questions and saying it's hard, the guide linked in the instructions tells you everything. Including youtube videos of how to beat every level...
This is what a tower defense game SHOULD be. It's difficult, and beating every level takes strategy and knowing the towers inside/out. It's a little repetitive, as each level just tacks on extra levels and you can use the same killzone tactics in every level. But VERY good game design and balance. 5/5, I hope you make more games.
I really really hate these games. Isn't the entire point to pretend like you're playing the song, which a qwerty keyboard sort of destroys? So it's just a really piece of crap "tap in order" game? Why the hell would anyone on the planet play this game on purpose. 1/5 for being retarded enough to make 3 versions.
The same reasons that Achilles sucks makes this sucks, people have all commented on it. Buggy, random, luck-based combat sucks. There's no skill, even with the perfect system it's just luck. That... sucks. The badges can just sit there.