It's not that old, is it?  xD

I wish I could make a video of the platformer I tried to create, but the software I currently have disables my "accept" keys for some strange reason.  - -;;;

Terrain ID's can do so many things here's to name a few:

another thing you can try out for yourself is making a psuedo 3d engine using the terrain ID's.  The terrain ID's correspond to the height of the coordinate.  with some coding, when you approach an edge you may fall off the cliff.  Done it myself, the engine is lost.

another thing with terrain ID's turn them into paths, that the NPC's can have a choice to take when it looks around.  so it's not just simply following orders of going up and around, but now it has some life to it.

one other thing use terrain ID's to indicate hot spots, say there's a hotdog stand, if an NPC is randomly walking around and find to the left of it is a hot dog stand, it can interact with it somehow.  Depending on the action you give it, you could have the NPC rob the hotdog stand, or another NPC buy a hotdog, or another NPC pee on it.  And you can give random drawing to just ignore the hotdog stand, so it's not like the NPC's are robots who need to consume every time they see a hotdog stand.

Terrain ID's are good stuff.

Another huge problem with rm2k/3 is how pictures can be moved.  Moving a picture requires knowing what number it is while in the programming step, instead of being able to move the picture based on the number in the variable.  I remedied this in the tech demo by create an objected oriented system that used pictures as objects were created.  So, for example, if a bush was hit, it would call the event, check to see the first available picture (lets say Picture 2), and then assign picture 2 to the bush animation.  Lets say a rupee drops from the bush, the event would be called, and picture 3 would be assigned as a rupee.  Lets now say that I shoot an arrow after I hit the bush, but before the rupee vanishes, the event would be called, and picture 2 is now free again to be used, so picture 2 is assigned to be an arrow.
The system is very useful to keep track of picture usage, and to create animations/objects of anything at any time.

This. I ran into that sort of problem a while ago and installed BananenJoe's DestinyPatch. It allows reference to a picture's actual X and Y coordinates and degrees of rotation, (not to mention adding a small scripting language). So I never actually made my own system to solve that. However, this dynamic allocation thing is really neat.

You can reference pictures by variable using Cherry's patches. Find it, download it, use it. Saves so many headaches.

Probably the most timesaving patch ever, but it doesn't have built-in pic ID allocation.

So the most 'advanced' thing I ever did was string together the Zelda meets Megaman battlesystem of Terra Nova. The RM2K engine is NOT MEANT to handle this sort of thing and I will NEVER use RM2K to do anything like this ever again. So many random issues all over the place, picture referencing being up there. Terrain ID was used to pretty much replace the entire default movement system. Also, the Call Event function is extremely useful. It can be used to nest commands for event movement into the actual enemy events to create a dynamic AI system where the sprite calls its own graphics functions while the daemon handles the communal AI. Also, having to make common events to handle data structures is a pain but not particularly hard. However, it leads to databases of thousands of variables. Oh, and between DestinyPatch and PicPointer, it came out looking very nasty:

yeah it's pretty fun, by adding the Z element, you can also implement wall jumps, and also hanging and strafing on ledges like a classic stealth game.  The place I got stuck at is implementing NPC's to handle the changes in elevation :/

I tried my hand at strategy games, and implementing a point and click pathfinding - is difficult and requires an advance algorithm.  But in the end it's accurate and the code isn't too much.  Dajisktra's I think was the name of the algorithm.

I got kind of ahead of myself, but you can implement jumping in 8 directions - which leads to wall jumps.

You guys are way ahead of me... I have no idea how to do that stuff.

Oh, I remember when the Modulus command made people confused...