Well, this is it: the Eggsterminator, the final boss of Sonic 2, tops my list (which means that it's tops among Sonic bosses in my book). This final boss is a nasty (at least if you don't know what you're doing) and very tedious fight. In fact, you very well have to worry about getting a time over, which costs you a life, while you're fighting this boss. The Eggsterminator takes several hits to bring down, uses different attack patterns depending on if you're facing it from the front or the back, flies off screen and tries to stomp you (hence the tediousness of the boss), and last but not least, you get to fight it with zero rings. Tip: You can hit the Eggsterminator up to 5 times before it launches off the screen for the first time.