Cake Invaders

You can increase your crew by collecting upgrades. The upgrades look like a circular rainbow that floats around the screen. You need to destroy them to collect the upgrades. In the later waves enemies will also carry upgrades. Keep in mind the upgrades are random so you will have to collect a few until you increase your crew to five.

Here's my full playthrough if you need any help surviving to the 12th wave.
I recommend going into the settings and turning the stick speed / sensitivity up so that way you can keep up with the faster moving enemies.
Intro 0:00
Explaining Achievements/Trophies 0:20
Wave 1 1:20
I'm not giving up! 11:00
Killing two birds with one stone 11:15
Having burnt one's boats 11:35