I was in the wiki pages, seeing the description on mini bosses and thought that there's no "final" mini bosses in any mission of all types in the game... well, not yet, anyway. So, I decided to do some editing to remove some mini bosses' descriptions in select wiki pages that are labeled "final", because, as you may, or may not know, there is no final mini boss in any Danger or other missions so far. If there was to be more than one mini boss in any new Danger Mission or otherwise added to Spiral Knights, the last mini boss would have been labeled "final", and then it would be considered to become the final mini boss in any Danger Mission that may have yet to have more than one mini boss to battle.
Point stating out, there's no final mini boss in any Danger Mission or otherwise yet. Just did some minor editing to get it out of my way.
Okay. I agree with you, that the phrase "final mini-boss" is misleading. But I suspect that whoever wrote the text meant that the mini-boss is the final encounter of the mission.