Rogue Legacy

*MISSABLE*

The reason I have flagged this achievement as missable is because there is no free roam or any way to access your playthrough again after you beat the final boss. Once you defeat the final boss, you'll be forced to start New Game+ immediately, and you will have to meet the requirements below all over again to get this achievement.

This achievement is for beating the remixed version of Herodotus. To access the remixed version of this boss, first you need to beat the standard version. Once done, you now need to find a Shrine Statue anywhere (on the current run or any subsequent run) and hope that the item you get from the Shrine is Herodotus's Obol. This is complete RNG, both with finding a Shrine and getting the Obol, but my experience was that the game was pretty good about granting you the Obol when you were after it. Just ensure that once you get the Obol, you don't accidentally replace it with a different item from a different Shrine. Once you die and are back outside, talk to Charon to give him the Obol. This will open the boss door for Herodotus in the Dungeon permanently (meaning on all subsequent runs, so you don't have to worry about beating it on this next run). Now, when you return to the boss door in the Dungeon and enter it, you'll be able to fight the remixed version, Astrodotus and Herodotus. Like all remixed boss fights, you play as a set character (so you don't need to wait until you level up more, and you can't build up your character to be stronger against the boss) and if you die, you're put right back outside the boss door with no penalty (you don't lose any money or progress, and can attempt again right away as many times as you want). 

This boss fight is the most unique one in the game, and probably the easiest. You play as a Dragon class, so you can fly, and the two bosses are flying around too, so the entire thing plays like the old arcade game Asteroids. You have two bosses to beat, and just like with the original fight, each time you destroy a blob it splits in two. All the little blobs will be flying around too then. Also, just like the game Asteroids, the screen wraps around from top to bottom and also side to side, giving you more room to dodge enemies. There aren't any Gravisors in this fight, so it's entirely about shooting enemies while dodging them. It'll likely take a couple tries, but that's it, and you shouldn't have many problems as long as you keep moving and take out enemies quickly. Once the boss is dead and you open the chest, you'll get a medallion piece and unlock this achievement.