was it?
Hardest Achievments
What about chatterbox? It requires 10000 activity points.
Or Puzzle Addict? It requires 10000 rated puzzles to correctly be solved.
Or Legend League? It requires entering the legends league.

All you would need to do is be in a high winning position and set it up a ladder checkmate where the king is on the 8th rank and when the king moves its mate
Ofc I haven’t tried it out yet but I will

You have to battle a bot in live chess to get it
It is currently impossible to get cuz of an error

All you would need to do is be in a high winning position and set it up a ladder checkmate where the king is on the 8th rank and when the king moves its mate
Ofc I haven’t tried it out yet but I will
You are correct, and your description is exactly how I did it. The hardest part is having an opponent that won't resign while you are setting it up.
In my opinion killer king and castle victory are the hardest to obtain.
There are also the holiday achievements, all of them are hard to obtain as the bots needed to get these achievements only come during Christmas time.