First of all, thank you kindly for your elaborative feedback! The game turned out to be much harder for other people since I got better at my game while playtesting it, I will pay attention to this phenomenon next time.
I added electro vest upgrade in the last minute with the intention of making the game easier for the last fight. Overall the game needs rebalancing.
I wasn't aware of the bug that you mentioned, thanks for that. Also when you click right mouse button or R after picking up an alien, you will lose it. This was supposed to drop the alien, but I neglected implementing it in order to meet the deadline.