Thanks for submitting - a good start to a good here. As others have mentioned the tower placing mechanism was not very intuitive but figured it out.
I was very confused about when a tower was needing repair and how to fix it. Ultimately was just clicking the fix tower button and replacing them. Real problem was when I made it to wave 12 and thought I had it in hand, suddenly all the enemies jumped to the end and I lost not sure what happened and did not have the will power to retry.
Keep at it.
I think its either because of lag, or because I gave the regeneration enemies a bit of invulnerability after they spawn. You could also be talking about the "last breath mechanic" where you have the heal the bastion by doing as much damage as you can in order to get a secondary win condition.
Another unclear mechanic could have been that the corrupted towers exploded and dealt damage to your bastion last second, and started the "last breath mechanic."
Thank you for playing, and if I cleared it up you should definitely try again!
