This is an absolutely fun game. The core gameplay is really solid, I made it all the way to wave 25.
My only piece of feedback is that the countdown theme could have been integrated a bit deeper. I noticed that the second frog explodes when its timer runs out, which is an awesome mechanic, expanding that idea so that more frogs have unique effects when their countdowns hit zero would be great, like a "last stand" where they shoot faster, or having the ice frogs freeze enemies around them when they expire.
I also think some more visual feedback could help understanding when we're taking damage or when the lily is about to expire, and also the balance could use some tweaks. Still, a fantastic submission. I really enjoyed this.