Here is another installment of exTRAPaganza, our Thursday over-the-top trap series.
Something like this came up in our campaign the other day, so I thought of this.
At least once per round, every character who is adjacent to an enemy has their tile shift enough to draw an attack of opportunity. Of course, they could hop off the tile with a ridiculously high acrobatics check to avoid provoking. If there’s a long line of enemies, they should move in front of all of them.