level.tilelayers[0].z and you

[Loriel]

Originally Posted by Inverness

Layer 0: the whole of the level, including what is under the bridge. Players are here.
Layer 1: This overlayes the bridge over players. Players walk under this if on layer 0.
[...]
When a player is going to walk onto a bridge, a script switches his layer to 1. This makes the player draw on the bridge and above any players walking below it.

This is pretty much what is already possible with NPCs and attachplayertoobj. It is also pretty ****ty because you could stand next to the bridge and instead of walking onto it, throw a bush right through it into the water.