Optional bosses are some of the most devious enemies in all of gaming. Just when you think you've bested a title's biggest challenge, watched the credits roll and breathed a sigh of relief that the punishment is finally over, you'll catch wind that there's an even bigger threat lurking somewhere you completely missed.
Even worse, these enemies are usually far more difficult than any other you've come up against, hiding in plain sight for only the bravest gamers to seek out. They can range from obvious, gigantic monsters bigger than skyscrapers such as Final Fantasy XV's devastating Adamantoise, or unassuming knights tucked behind convoluted unmarked quests that are far more deadly than they appear.
Either way, they are guaranteed to kick your arse at least once.
These are the guys that demanded you grind for hours just for the chance to be in their presence; the type of bosses who could pimp slap away 20 minutes of progress with a single blow.
Ultimately they're the ones you need to beat if you want to call yourself a gamer.