I got pawn killer in 3|0 Chess 960 as my opponent choose to promote h2 pawn to queen and I capture b7 pawn with my a6 pawn. My king was on c8, my opponent king on a8 with pawns on a7 and b7.
Killer Pawn Achievement
I got it by promoting a pawn to a queen i dont know if this is a feature or bug but good for hs i guess
I wasted 30 moves into forcing a pawn mate to get that achievement! Well, now I know that I just should have promoted to a queen and checkmate.
I also got it here: https://www.chess.com/analysis/game/live/81543197064?tab=review
It appears that if you checkmate with a pawn promoted to a queen on the turn of promotion, it will register as a pawn checkmate.
same here, that is how I got the achievement
A promotion into any piece resulting in mate or a pawn push delivering mate should trigger the killer pawn achievement.
Try killer king