Just finished this game with gold medals for all stages. My god this is the most unforgiving tower defense game I've ever played. The only two units you should use starting stage 3 are marines and rangers. You put two marines and rangers for the rest on the field. At stage 4 your units need to be at least lvl 3 and at least lvl 4 at stage 5. The only way for you to survive early onslaught is to buy plastic barricades and use medic droid. Get better barricades only when you have much more than enough money. When you encounter multiple green bugs (strongest enemy unit) remember to spam your only damaging skill and push skill, otherwise you will get owned, in your face style.
Be warned though, the game's bugged, it sometimes switches your droid to battle mode (i've killed many lvl 4's b/c of this QQ). Also, if you leave the game your stage progress won't be saved, so you'll have to finish all seven stages in one sitting.
I just beat the game, final boss is way too easy (due to hitbox bug), what a let down.
For those who don't know, this is a fan game of I Wanna Be The Guy. A bad one. On top of one of the worst collision detection and hitbox there can be in an indie game, this game merely imitates the form of IWBTG without having the soul of IWBTG, which is black humor. It also lacks all the wonderful and well-placed references and music IWBTG has. The level design is too simple, it feels like an unfinished game. Lastly, I'm calling the level designer out on almost copying one of the rooms from I Wanna Be The Fangame. That sh!t is too close, man. Your lack of effort and ethics is stunning.
The mouse control is so poorly designed, but I managed to finish the game eventually. The trick is to leave the furthest planet the last to destroy, and make all planets on the diagonal line fortresses. This would give you enough time to mass the strongest unit (the big gray ship) at home planet, which is where you duke it out with the mothership and win.
 "Mars Commando"){kind=icon}
 "Twisted Military"){kind=icon}
 "I Wanna Be The Flash Game"){kind=icon}
 "I wanna be the guy 0.21 BETA"){kind=icon}
 "Galactic Invaders: Build and Conquer the Universe!"){kind=icon}
 "Cloudstone"){kind=icon}