Nothing like a little robot-on-robot violence, right? Kongregate's newest game on Android had a good run over on iOS and the name tells you pretty much everything you need to know about it – Endless Boss Fight. You fight bosses, endlessly.
Your main character is a little punching robot that has to do battle with big, heavily armed robot boss machines. You duck, weave, and punch your way through one after another until you lose. There are missions to complete along the way, along with rewards. It's a bit like an endless runner in that respect. In addition to the main gameplay, you can create and upgrade your own boss character, which is then battled by other humanoids in the multiplayer area. This all happens even when you're offline, so you are advised to keep it upgraded.
Of course, all the upgrades for your robots cost coins. There are two types of currency in this game, and you'll need to spend real money on the rare type if you want to do well. Some folks are okay with that, but I'm not one of those people.