Hello. Agent Pugin94 here! I will tell you advice on how to beat some enemies on System Defender. First, let's start with the Ultimate Protobot. Through out the entire game, he says stuff like, "Commencing attack pattern Omicron," and other. Well, let me tell you THIS, put up a LOT of Yellow Cannons and Purple Cannons, and make sure to upgrade them, or Protobot will win. Look below, and you'll see what I mean.
If you use my strategy for beating him, then it should work. And one thing I need to say, I put up Yellow Cannons a lot because I like Yellow Bots. But people ask me, "If you like them, why are you DESTROYING them?". It's obvious that I like them, but just because I do I don't want them to destroy the EPF mainframe. Oh, I like EVERY bot, but Yellow is the best. Purple is my SECOND favorite.
Let's get on with the advice. Protobot is very powerful, and he's hard to beat. Most of the CPCT beat him on their first try, but some members of the CPCT have trouble doing it, like Karata Ninja and Gunter143. (Gunter143 hasn't beat the Test Bots!).