Since I've done this before, it's possible to do this utilizing a couple of plugins to achieve a very similiar result.
1) Grab
Tsukimi's Pixi Filter Controller plugin.
2) Save the image attached below to your "img/picture" folder (make sure it's named "DisplacementMap.png").
3) Go in to the plugins config and put "DisplacementMap" in the blank space beside "Displacement Map Image" (can be skipped if it's left as is by default.
4) Make an event on the map and add the following "Plugin Command" calls.
createFilter displace1 displacement 2
setFilter displace1 1 0 2
createFilter displace2 displacement 2
setFilter displace2 -1 0 2
createFilter godrays godray-np 2
setFilter godrays 408 -100 0.5 2.4 1
5) Use a "Tint Screen" command with the following values.
Red -150
Green -50
Blue 0
Gray 100
5) Place an "Erase Event" at the end of the event and set to a "Parallel" Trigger type.
If you want to add a "caustic" like effect to the tilemap, you'll need another plugin.
1) Grab
Galv's Layer Graphics plugin.
2) Go to your "img" folder and create a folder called "layers".
3) Save a copy of the "DisplacementMap.png" in to the "layers" folder.
4) Place the following "Plugin Command" calls (replace "X" with the map number).
LAYER X 1 DisplacementMap 0.0 0.4 60 10 0 0 1
LAYER X 2 DisplacementMap -0.6 -0.5 60 10 0 0 1
LAYER X 3 DisplacementMap 0.5 -0.6 60 10 0 0 1
LAYER REFRESH