Video game bosses are a cheeky bunch, aren't they?
Sure, nowadays we have cutscenes and flavor text to tell you who you're up against, but back in the old days they'd often just pop up out of nowhere. you may think those days are behind us, but old habits die hard. Especially with the final boss.
The final challenge of a video game can often come as a massive shock to the player, because you're suddenly fighting someone you had no idea was even a thing, convinced you were fighting someone else you'd spent the whole game building up to. Instead, the game goes "psych!" and replaces your arch enemy with some other random schmuck.
Whether they're the final boss of the main story mode, the "true" final boss accessed through jumping through various hoops, or just a secret boss that represents the greatest challenge in the game, these are the ultimate bosses of their respective games.
And yet, said games felt no need to bring that up at all, making you wonder what the hell they're doing here in the first place.
10. Calasmos - Dragon Quest XI
This one sits at the bottom of the list due to Calasmos TECHNICALLY showing up before the final battle, but in a side quest that almost everyone misses due to the game never telling you "oh by the way important plot stuff is happening at Galapolis maybe you should stop by". Of course, due to Dragon Quest's nature of being a celebration of tried and true JRPG tropes, it shouldn't be that surprising that you kick god in the teeth at the end.
Calasmos is an eldritch god of emptiness, born at the dawn of time who seeks to return everything to the nothingness that encompasses his being. Originally, the other big bad, Mordegon, stopped Calasmos from returning after he took over the world since it's kinda hard to rule the world when there is no world.
But then you go back in time and erase the entire second act of the game from ever happening, meaning that Calasmos is reborn unhindered. Oops.
And so the game's true final boss is this giant Cell-from-DBZ looking dude whom the hero has somehow less connection to than he did with Mordegon, making the whole thing feel utterly transparent.