Are you ready... for the most horrific experience you've ever had in your life.... THE FALLEN BASIC TANK!
The Fallen Basic Tank is a boss that spawns after 5 fallen tanks spawn in a row (yep). It has 1 HP and drops 3.14159 XP when killed. It can be one-shot with a basic Tank. It's bullets to 1 damage, and is essentially nothing to defeat. It is the easiest boss in the game.