This might seem obvious, but you need to win 25 multiplayer matches in the "Survival" game type. "VS Survival" does not count.
You also need at least one other player in the match for it to count, creating a private multiplayer match and playing solo does not award credit. Good news is that it tracks on the Xbox achievement. Progress is awarded the moment the boss is killed.
Quickest way to get this is Normal/Short, but even still you're looking at around 15-20 mins per match if everyone needs the trader plus loading times, making this achievement around the 6 hour mark to obtain (at best).