M to Mute, N to Unmute for those of you that missed it on the main screen.
P to pause, U to unpause
Space bar to de-select
This is a 10 level Tower defense game with 9 towers(5 unlockable with tech level).
Ultimate Towers need gems to build so you are limited in the amount you can build.
Yes, the first 5-6 levels are pretty easy, use them to rack up XP and upgrade. You will need those upgrades for the last few levels.
There is an interest of 4% at the beginning of every wave so saving up is worth it especially in the later levels.