Munchkin: Quacked Quest

As with many achievements in this game, progress is reset when you return to the dashboard, so you must meet the entire requirement in 1 play session, but not necessarily one dungeon.

The safest way to do this is to start up a 1-hour dungeon (You can change the dungeon timer by accessing the upper right kiosk in the main hub). Use a 2nd controller for player 2.
Play until you come across a level with a bottomless pit. They are usually blue glowing openings in the floor, similar to ice, but you fall through!
You have to push 25 enemies into these pits using shield bash () or charge (). The achievement unlocks as soon as the 25th enemy is defeated in this way, so you can end the run after completion.

Not necessary, but before a run you may draw the enemy modifier "trash mobs." This makes all enemies rats or chickens. The layout "hole-ish" adds lots of pits. Both can make this a lot quicker.

You may want to play shorter 5-8 minute runs to also work on unlocking cards. I had the game crash to the dashboard 3 times in about 15 runs, always as the game was trying to load a boss room, so beware.